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lECHHICAl LIBRARY 
of the 

armed forces 

SPECIAL WEAPOMS PROJECT 




SUMMARY TECHNICAL REPORT 
OF THE 

NATIONAL DEFENSE RESEARCH COMMITTEE 




UNCLASSiFIED 





Manuscript and illustrations for this volume were prepared 
for publication by the Summary Reports Group of the 
Columbia University Division of War Research under con- 
tract OEMsr-1131 with the Office of Scientific Research and 
Development. This volume was printed and bound by the 
Columbia University Press. 

Distribution of the Summary Technical Report of NDRC 
has been made by the War and Navy Departments. Inquiries 
concerning the availability and distribution of the Summary 
Technical Report volumes and microfilmed and other refer- 
ence material should be addressed to the War Department 
Library, Room lA-522, The Pentagon, Washington 25, D. C., 
or to the Office of Naval Research, Navy Department, Atten- 
tion : Reports and Documents Section, Washington 25, D. C. 

Copy No. 

i 1 


This volume, like the seventy others of the Summary Tech- 
nical Report of NDRC, has been written, edited, and printed 
under great pressure. Inevitably there are errors which have 
slipped past Division readers and proofreaders. There may 
be errors of fact not known at time of printing. The author 
has not been able to follow through his writing to the final 
page proof. 

Please report errors to : 

JOINT RESEARCH AND DEVELOPMENT BOARD 
PROGRAMS DIVISION ( ST ERRATA) 

WASHINGTON 25, D. C. 

A master errata sheet will be compiled from these reports 
and sent to recipients of the volume. Your help will make 
this book more useful to other readers and will be of great 
value in preparing any revisions. 




SUMMARY TECHNICAL REPORT OF DIVISION 6, NDRC 


R D B 




VOLUME 5 


\\%\o 

3 


MAGNETIC AIRBORNE 
DETECTOR PROGRAM 


OFFICE OF SCIENFIFIC RESEARCH AND DEVELOPMENT 
\^\NNEVAR BUSH, DIRECTOR 

NATIONAL DEFENSE RESEARCH COMMITTEE 
JAMES B . C O N A N T , CHAIRMAN 

DIVISION 6 
JOHN T . TATE, CHIEF 


WASHINGTON, D. C., 1946 


NATIONAL DEFENSE RESEARCH COMMITTEE 


James B. Conant, Chairman 
Richard C. Tolman, Vice Chairman 
Roger Adams Army Representative^ 

Frank B. Jewett Navy Representative- 

Karl T. Compton Commissioner of Patents^ 

Irvin Stewart, Executive Secretary 


lArmi/ representatives in order of service: 

Maj. Gen. G. V. Strong Col. L. A. Denson 

Maj. Gen. R. C. Moore Col. P. R. Faymonville 

Maj. Gen. C. C. Williams Brig. Gen. E. A. Regnier 

Brig. Gen. W. A. Wood, Jr. Col. M. M. Irvine 

Col. E. A. Roiitheau 


^Navy representatives in order of service: 

Rear Adm. H. G. Bowen Rear Adm. J. A. Furer 
Capt. Lybrand P. Smith Rear Adm. A. H. Van Keuren 
Commodore H. A. Schade 
^Commissioners of Patents in order of service: 
Conway P. Coe Casper W. Ooms 


NOTES ON THE ORGANIZATION OE NDRC 


The duties of the National Defense Research Committee 
were (1) to recommend to the Director of OSRD suit- 
able projects and research programs on the instrumen- 
talities of warfare, together with contract facilities for 
carrying out these projects and programs, and (2) to 
administer the technical and scientific work of the con- 
tracts. More specifically, NDRC functioned by initiating 
research projects on requests from the Army or the 
Navy, or on requests from an allied government trans- 
mitted through the Liaison Office of OSRD, or on its own 
considered initiative as a result of the experience of its 
members. Proposals prepared by the Division, Panel, or 
Committee for research contracts for performance of 
the work involved in such projects were first reviewed 
by NDRC, and if approved, recommended to the Director 
of OSRD. Upon approval of a proposal by the Director, 
a contract permitting maximum flexibility of scientific 
effort was arranged. The business aspects of the con- 
tract, including such matters as materials, clearances, 
vouchers, patents, priorities, legal matters, and admin- 
istration of patent matters were handled by the Execu- 
tive Secretary of OSRD. 

Originally NDRC administered its work through five 
divisions, each headed by one of the NDRC members. 
These were : 

Division A — Armor and Ordnance 
Division B — Bombs, Fuels, Gases, & Chemical Problems 
Division C — Communication and Transportation 
Division D — Detection, Controls, and Instruments 
Division E — Patents and Inventions 


In a reorganization in the fall of 1942, twenty-three 
administrative divisions, panels, or committees were 
created, each with a chief selected on the basis of his 
outstanding work in the particular field. The NDRC 
members then became a reviewing and advisory group to 
the Director of OSRD. The final organization was as 
follows: 

Division 1 — Ballistic Research 

Division 2 — Effects of Impact and Explosion 

Division 3 — Rocket Ordnance 

Division 4 — Ordnance Accessories 

Division 5 — New Missiles 

Division 6 — Sub-Surface Warfare 

Division 7 — Fire Control 

Division 8 — Explosives 

Division 9 — Chemistry 

Division 10 — Absorbents and Aerosols 

Division 11 — Chemical Engineering 

Division 12 — Transportation 

Division 13 — Electrical Communication 

Division 14 — Radar 

Division 15 — Radio Coordination 

Division 16 — Optics and Camouflage 

Division 17 — Physics 

Division 18 — War Metallurgy 

Division 19 — Miscellaneous 

Applied Mathematics Panel 

Applied Psychology Panel 

Committee on Propagation 

Tropical Deterioration Administrative Committee 


CONFIDENTIAL 


l/i6rai y of O'ongrcss 



2015 49(*‘)49 


NDRC FOREWORD 


A s EVENTS of the years preceding 1940 re- 
^ vealed more and more clearly the serious- 
ness of the world situation, many scientists in 
this country came to realize the need of organ- 
izing scientific research for service in a national 
emergency. Recommendations which they made 
to the White House were given careful and sym- 
pathetic attention, and as a result the National 
Defense Research Committee [NDRC] was 
formed by Executive Order of the President in 
the summer of 1940. The members of NDRC, 
appointed by the President, were instructed to 
supplement the work of the Army and the Navy 
in the development of the instrumentalities of 
war. A year later, upon the establishment of the 
Office of Scientific Research and Development 
[OSRD], NDRC became one of its units. 

The Summary Technical Report of NDRC is 
a conscientious effort on the part of NDRC to 
summarize and evaluate its work and to present 
it in a useful and permanent form. It comprises 
some seventy volumes broken into groups cor- 
responding to the NDRC Divisions, Panels, and 
Committees. 

The Summary Technical Report of each Divi- 
sion, Panel, or Committee is an integral survey 
of the work of that group. The first volume of 
each group’s report contains a summary of the 
report, stating the problems presented and the 
philosophy of attacking them, and summarizing 
the results of the research, development, and 
training activities undertaken. Some volumes 
may be “state of the art” treatises covering 
subjects to which various research groups have 
contributed information. Others may contain 
descriptions of devices developed in the labora- 
tories. A master index of all these divisional, 
panel, and committee reports which together 
constitute the Summary Technical Report of 
NDRC is contained in a separate volume, which 
also includes the index of a microfilm record of 
pertinent technical laboratory reports and ref- 
erence material. 

Some of the NDRC-sponsored researches 
which had been declassified by the end of 1945 
were of sufficient popular interest that it was 
found desirable to report them in the form of 
monographs, such as the series on radar by 
Division 14 and the monograph on sampling 
inspection by the Applied Mathematics Panel. 
Since the material treated in them is not du- 


plicated in the Summary Technical Report of 
NDRC, the monographs are an important part 
of the story of these aspects of NDRC research. 

In contrast to the information on radar, 
which is of widespread interest and much of 
which is released to the public, the research on 
subsurface warfare is largely classified and is 
of general interest to a more restricted group. 
As a consequence, the report of Division 6 is 
found almost entirely in its Summary Technical 
Report, which runs to over twenty volumes. 
The extent of the work of a Division cannot 
therefore be judged solely by the number of 
volumes devoted to it in the Summary Technical 
Report of NDRC: account must be taken of 
the monographs and available reports published 
elsewhere. 

Any great cooperative endeavor must stand 
or fall with the will and integrity of the men 
engaged in it. This fact held true for NDRC 
from its inception, and for Division 6 under the 
leadership of Dr. John T. Tate. To Dr. Tate and 
the men who worked with him — some as mem- 
bers of Division 6, some as representatives of 
the Division’s contractors — belongs the sincere 
gratitude of the Nation for a difficult and often 
dangerous job well done. Their efforts contrib- 
uted significantly to the outcome of our naval 
operations during the war and richly deserved 
the warm response they received from the Navy. 
In addition, their contributions to the knowl- 
edge of the ocean and to the art of oceano- 
graphic research will assuredly speed peacetime 
investigations in this field and bring rich bene- 
fits to all mankind. 

The Summary Technical Report of Division 6, 
prepared under the direction of the Division 
Chief and authorized by him for publication, 
not only presents the methods and results of 
widely varied research and development pro- 
grams but is essentially a record of the un- 
stinted loyal cooperation of able men linked in 
a common effort to contribute to the defense 
of their Nation. To them all we extend our 
deep appreciation. 

Vannevar Bush, Director 
Office of Scientific Research and Development 

J. B. CONANT, Chairman 
National Defense Research Committee 


CONFIDENTIAL 


V 


4 






I - ‘‘«V 

w* 

f ■ - 

I 




f 




•i 


i 





FOREWORD 


B y 1941, IT WAS becoming increasingly clear 
that the airplane was a powerful weapon 
for antisubmarine search and attack. This was 
true even with no detection means other than 
visual sighting and no ordnance other than 
conventional bombs or depth-charges. Radar, 
particularly micro-wave radar, was to extend 
the efficiency of search operations for surfaced 
U-boats particularly during periods of low 
visibility and darkness. But no means existed 
for “seeing’’ a submerged submarine from air- 
craft. To remedy this situation the Division 
supported a very considerable program of re- 
search and engineering development on a re- 
liable magnetic airborne detector [MAD] 
having adequate sensitivity to detect sub- 
marines positively at operationally useful 
ranges. 

The concept of using the magnetic disturb- 
ance or anomaly created by the steel hull of a 
submarine to detect its presence is an old one. 
It had long been employed as a method of 
harbor protection. The problem here, however, 
was the difficult one of adapting these instru- 
ments, sensitive to both movement and orienta- 
tion, for use on rapidly moving patrol aircraft. 

In 1940 the Gulf Research and Development 
Company, supported by NDRC contract, under- 
took to adopt a sensitive magnetometer of their 
design to this purpose. Also the British were 
attempting to exploit other methods. 

Division 6 promptly began a thorough study 
under the able leadership of Dr. L. B. Slichter, 
of all known methods of instrumentation. It 
soon became apparent that a sensitive magne- 
tometer being developed by the Gulf Company 
under a separate NDRC contract offered the 


greatest probability of success. To develop fully 
the possibilities of the device in a form suitable 
for service use, the Division, under contract 
with Columbia University, set up the Airborne 
Instruments Laboratory where most of the 
further development work of this device was 
concentrated. 

For the preparation of this report describing 
the activities and accomplishments of this de- 
velopment program, the Division is indebted to 
a number of persons, including H. R. Skifter, 
V. V. Vacquier, R. F. Simons and J. T. Wilson; 
and the Division 6 editorial staff of the Colum- 
bia Summary Reports Group under J. S. Cole- 
man. 

No attempt can be made here to credit all 
individuals and organizations which contributed 
to the successful outcome of this project. The 
basic contribution of the Gulf Research and 
Development Company has already been men- 
tioned. This included the magnetometer de- 
veloped by Dr. V. V. Vacquier. Mr. T. E. Shea 
had general supervision for some time of the 
development program which was under the 
immediate direction of Dr. D. G. C. Hare. 

This development proceeded in close liaison 
with the Army and Navy. As conditions per- 
mitted, facilities for tests were freely provided. 
Special mention should be made of the vigorous 
interest of Admiral C. C. Rosendahl, C. 0. of 
the Naval Air Station at Lakehurst and of the 
assistance which Lt. Comdr. J. B. Joyce of the 
Bureau of Aeronautics gave in matters of pro- 
curement and manufacture. 

John T. Tate 
Chief, Division 6 


CONFIDENTIAL 


Vll 



PREFACE 


T he present volume is an attempt to sum- 
marize in orderly fashion the work done by 
Division 6 contractors in the development of 
Magnetic Airborne Detector systems. Most of 
the Division effort was directed towards im- 
proving and adapting the Vacquier magnetom- 
eter circuit to aircraft use. One chapter is 
therefore entirely devoted to explanation of 
some of the fundamentals governing the be- 
havior of this form saturated-core magnetom- 
eter. While it is obviously impossible in the 
allotted space to treat in detail all of the re- 
search and development that have supported 
this investigation, it is believed that the ma- 
terial presented should facilitate understanding 
of the operation of this instrument. 

The remaining chapters are concerned with 
the design, circuits, installation, and operation 
of the several instruments developed by the 
Airborne Instruments Laboratory [AIL] of the 
Columbia University Division of War Research 
[CUDWR] at Mineola, L. I. This program, 
which accounted for the bulk of the Division's 
activity in this field, culminated in the 
AN/ASQ-1 and AN/ASQ-IA systems, both of 
which were installed and saw active service in 
numerous patrol aircraft, as well as the 
AN/ASQ-2 dual system, designed to provide 
automatic operation, which was put into experi- 
mental Service use. Mention is also made of the 
preliminary work done on the AS/ASQ-3 sys- 
tem by the Bell Telephone Laboratories prior 


to the transfer of the project to direct Navy 
sponsorship. 

The technical memoranda and reports upon 
which much of this volume is based were 
originally prepared by the scientists and 
engineers employed in these investigations. It 
is regretted that the limitations of space make 
it impossible to allocate individual credit for 
their many accomplishments. This material 
was collected and furnished to the CUDWR 
Summary Reports Group [SRG], by J. T. 
Wilson of the AIL staff. 

In addition, certain new material on the be- 
havior of saturated-core magnetometers was 
made available by V. Vacquier of the Sperry 
Gyroscope Company. Other contributions were 
received from E. H. Colpitts, Chief of Section 
6.1, NDRC, and from R. H. Simons of AIL. 
Final editing and arrangement of material was 
largely carried out by C. B. Ellis of the SRG 
staff, with some assistance from J. S. Coleman 
of the same group. To all of the above and to 
the staffs of the Gulf Research and Develop- 
ment Company, the Bell Telephone Labora- 
tories, the Naval Ordnance Laboratory, and the 
Airborne Instruments Laboratory are due the 
grateful thanks of the Division and its editors 
for their helpful cooperation in making avail- 
able the source material, drawings, and photo- 
graphs required for the volume, and in furnish- 
ing constructive criticism of the present work. 

J. S. Coleman 


LX 


CONFIDENTIAL 





CONTENTS 


CHAPTER PAGE 

1 Introduction 1 

2 Saturated-Core Magnetometers 11 

3 The AN/ASQl Detection Equipment ... 20 

4 MAD Signal Studies 43 

5 Automatic Firing Systems 65 

6 Installations of MAD in Aircraft 83 

7 Training Devices and Experimental Equipment 108 

8 Use of MAD for Land Targets 128 

Glossary 135 

Bibliography 137 

Patent Applications and Invention Reports . . 143 

Contract Numbers 146 

Project Numbers 147 

Index 149 


CONFIDENTIAL xi 


i 





Chapter 1 

INTRODUCTION 


I N THE SPRING of 1941, Section C-4, later Divi- 
sion 6, of. the National Defense Research 
Committee [NDRC] undertook the further 
active development of methods for detecting 
and locating submerged submarines. That air- 
craft would play an important part in antisub- 
marine warfare was clearly recognized. This 
seemingly required that aircraft should be able 
to detect and locate submerged as well as sur- 
faced submarines. The recognition of this need 
led Section C-4 to undertake the further devel- 
opment of the magnetic airborne detector, the 
subject of this volume, and somewhat later, to 
undertake the development of the aircraft radio 



Figure 1. One type of main coil with trimmers 
developed for use in the magnetic gradiometer 
method. 

sono buoy, reported upon in Volume 14 of Divi- 
sion 6. With respect to the art pertinent to the 
project undertaken by Section C-4, reference 
will be limited to two developments then under 
way. 

The British, as had been learned through 
Navy and NDRC channels, were attempting the 
development of magnetic airborne gear for the 
detection of submerged submarines, and com- 
plete information as to their plans had been 
made available in part through a visit to Great 
Britain by American scientists early in 1941. 

Even more importantly, the Gulf Research 
and Development Company had, in November 
1940, begun work independently on sensitive 


magnetic devices directed toward geophysical 
prospecting and military objectives. This de- 
velopment promptly produced an instrument 
commonly referred to as the Vacquier mag- 
netometer, and its employment on aircraft for 
submarine detection was suggested and consid- 
ered. 

In February 1941 the Gulf Research and 
Development Company arranged for the co- 
operation of the Sperry Gyroscope Company, 
and a test flight of the first model was made in 
a Sperry plane late in that month. Subsequent 
to this the Gulf Company worked under an 
NDRC contract under direction of Section 
D-3 until June 30, 1941, when, as of July 1, 
1941, direction of magnetic airborne detector 
development was taken over and continued by 
the newly organized Section C-4. 

In addition to continuing the work by the 
Gulf Research and Development Company, Sec- 
tion C-4 in its initial development program, 
under contracts with Columbia University, the 
Western Electric Company, and the General 
Electric Company, included the development of 
means for locating submerged submarines from 
aircraft by detecting the magnetic anomaly set 
up by the ferromagnetic mass of the submarine. 
The technical group assigned to this project 
under the Columbia University contract soon 
came to be designated as the Airborne Instru- 
ments Laboratory [AIL] and remained in ac- 
tive operation until the end of 1944. 


NATURE OF PROBLEM 

To detect a submerged submarine from an 
aircraft by the method under consideration re- 
quires the measurement of the small distortion 
of the earth’s magnetic field caused by the pres- 
ence of the submarine. The earth’s magnetic 
field has a total intensity of about 60,000 
gammas (1 gamma = 10“^ oersted) and the 
distortion at a few hundred feet distance from a 
submarine is but a few gammas. When this 
development was undertalcen, devices capable 


CONFIDENTIAL 


I 


2 


INTRODUCTION 


of measuring variations in magnetic fields of 
less than 1 gamma were available, but they 
were not immediately adapted to use in aircraft 
for the following reason. Since the earth’s mag- 
netic field is a vector quantity, relative motions 
between it and the sensitive axis of the measur- 
ing device will produce indications of changes 
in field intensity, and either these indications 
or signals must be neutralized or these relative 
motions must be eliminated. From the begin- 
ning of this development, the major problem 


was solved is indicated by the performance of 
the detection equipment finally developed. This 
had a background noise level of about 0.2 
gamma under conditions of reasonably straight 
and level flight in a magnetically quiet area. If 
the magnetic fields due to the aircraft itself are 
properly compensated, the spurious indications 
resulting from rapid plane maneuvers are not 
over a few gammas. Thus the equipment is 
capable in even flight of detecting a submarine 
where the magnetic anomaly produced by its 



-8.r 



was recognized to be the elimination of the 
effect of those aircraft motions which give rise 
to spurious signals. Also, another source of 
spurious signals is the effect of the magnetic 
fields produced by the aircraft itself. To avoid 
spurious signals from this cause, it is necessary 
to select the most favorable location for the 
measuring device and quite commonly to pro- 
vide in addition magnetic compensation. (See 
Chapter 6.) 

How completely the major problem above 


presence is only a few gammas. For the average 
submarine, this range will be about 500 feet. 


12 METHOD PROPOSED BY BRITISH 

One of two methods may be employed to 
determine the distortion of the earth’s magnetic 
field resulting from the presence of a submarine 
or other ferromagnetic mass. The first method 
employs a magnetic gradiometer which when 


CONFIDENTIAL 



METHOD PROPOSED BY BRITISH 


3 


mounted upon an airplane in flight measures 
the space rate of change of the magnetic gradi- 
ent. In the second method a magnetometer 
measures directly any anomalies in the mag- 



Figure 3. The MAD Mark I equipment. 


netic field. While the first method was not de- 
veloped to the stage of Service use, brief men- 
tion of it will be made at this point. 

By early in 1941, the British had developed 
a two-coil magnetic gradiometer system capa- 
ble under favorable conditions of detecting a 
submarine at a range of 200 feet. It was obvi- 
ous to the British that this range was too small 
to be of operational value. The feeling ex- 
pressed to NDRC representatives was that if 
the range could be doubled, the instrument 
would probably be of great value, but the in- 
herent difficulty of accomplishing this by the 
British method is indicated by the following 
analysis. 

The British experimental equipment con- 
sisted of two large inductance coils about a foot 
in diameter, mounted coaxially in a framework 
and separated about 8 feet. Each coil was as 
nearly as possible identical to its mate and was 
wound with a large number of turns, the prod- 


uct of the number of turns times the area of 
the coil in cm^ being between 10^ and 10®. The 
two coils were connected in opposition, and with 
a suitable detector they form a magnetic gradi- 
ometer. As to expected performance of such a 
system, a submarine is very nearly equivalent 
to a magnetic dipole and the magnitude of such 
a field falls off as the third power of the dis- 
tance.^ An airplane carrying this balanced coil 
system will measure the space rate of change 
of the magnetic gradient which varies with the 
inverse fifth power of the distance. Thus to in- 
crease the working range from 200 feet to 400 
feet necessitates an increase in the signal-to- 
noise ratio or in the airplane speed by a factor 
of 32. 

To continue exploration upon the possibilities 
of this gradiometer method certain work was 
undertaken by Section C-4. Investigations indi- 
cated that a large portion of the background 
noise was due to deflections of the coil mount- 
ings. Therefore, the first step was to devise a 
coil mounting sufficiently rigid to keep the elec- 
trical axes of the two coils parallel within ex- 
tremely close limits. This work on design of 
mountings (see Figures 1 and 2) was under- 
taken at the Bell Telephone Laboratories and 



Figure 4. Gyroscope with magnetometer coils 
developed by General Electric Company. 


also at the California Institute of Technology. 
Another step was initiated, namely, the con- 
struction of amplifiers to aid in detection of the 
low frequency and low voltage signals involved. 


CONFIDENTIAL 





4 


INTRODUCTION 


Because of the promising results being ob- 
tained with the Gulf Research and Develop- 
ment Company’s equipment employing the Vac- 
quier magnetometer, research on this method 
was terminated in November 1941. 


July 1941 an experimental instrument designed 
by the Gulf Company and utilizing a gyro fur- 
nished by the Sperry Gyroscope Company was 
available for test. This instrument employed the 
Vacquier saturated-core magnetometer and 



Figure 5. MAD Mark V head assembly. 


13 DEVELOPMENT OF MAGNETIC 
AIRBORNE DETECTOR 

Although later chapters of this volume de- 
scribe the major developments in detail it seems 
appropriate to include in this introductory 
chapter a brief survey of the work between 
June 1941 and its termination. It will appear 
that while development was undertaken in 1941 
under contracts with several agencies, after 
about one year NDRC development was concen- 
trated in the Airborne Instruments Laboratory 
[AIL] operated by Columbia University. 

^ Gulf Research and Development 
Company 

Reference to the work of this company prior 
to June 30, 1941, has already been made.^'^ In 


gyroscopic stabilization. Flight tests in which a 
representative of the Navy and of the Airborne 
Instruments Laboratory participated were 
made. These tests showed promise and indi- 
cated the direction further development should 
take. 

Continuing development for several months, 
the Gulf Company produced the magnetic air- 
borne detector [MAD] Mark 1. Essentially it 
comprised a saturated-core magnetometer of 
the type to be described in Chapter 2, which 
had the sensitive element oriented in the direc- 
tion of the earth’s magnetic field to measure 
any anomalies caused by magnetic objects. The 
element was mounted on the frame of a gyro 
horizon with the angle between the magnetom- 
eter element and the gyro horizon set manu- 
ally to the magnetic dip prevailing in the search 
area. The whole system was mounted for orien- 


CONFIDENTIAL 


DEVELOPMENT OF MAGNETIC AIRBORNE DETECTOR 


5 


tation in azimuth by a shaded pole motor. The 
direction and amount of rotation of this motor 
were controlled by a second saturated-core mag- 
netometer mounted on the gyro horizon with 
its axis along the magnetic east-west. When the 
detector element was in line with the earth’s 
field, this magnetometer was normal to the 
field and therefore had no output signal. When 
the azimuth was not zero, the east-west mag- 
netometer gave a signal which controlled the 
current in the shading field windings of the 
motor through suitable relays to bring the de- 
tector element again into line. 

This equipment was tested in November 1941 
at Quonset Point, and the flights made at that 
time showed that signals could be obtained from 
S-type submarines at altitudes of more than 
400 feet. In straight and level flight of a PBY 
airplane the equipment, mounted in the hull, 
had a noise level of approximately 3 gammas. 
Its inherent noise level on the ground in a 
quiet location was about 0.5 gamma. Contrary 
to expectations, tests made in conjunction with 
our own submarines indicated that it was nec- 
essary for the equipment to function at all times 
during flight, including even the most rapid 
maneuvers. For several reasons, the noise level 
on the Vacquier equipment was unreasonably 
high when the airplane was maneuvering. The 
primary cause of this high background noise 
was that the gyroscope being held vertical by 
gravity would process from the centrifugal 
force during a turn and give rise to a large 
anomalous signal when straightening out. Con- 
tributing also to this background noise were the 
local fields due to the aircraft’s ferromagnetic 
and conducting parts. During the weeks follow- 
ing the first tests of this equipment, efforts were 
made with considerable success to reduce these 
sources of noise by ‘‘deperming” hard steel 
members of the plane and compensating for the 
effects of others. However, it was soon realized 
that little could be done about the inherent limi- 
tation of the gyroscope. 

In December 1941 at the request of the Com- 
manding Officer of Lakehurst Naval Air Sta- 
tion, the Mark I MAD was installed in a blimp 
and was in Service use until the late summer of 
1942. 

Although the limitations of performance of 


the Mark I were clearly indicated and the means 
for improvement visualized, the urgency of the 
submarine problem was at the moment such 
that Gulf was requested to defer further devel- 
opment and to make a number of Mark II in- 
struments differing from Mark I only in minor 
improvements which could be quickly incor- 
porated. The first Mark II unit was delivered in 
February 1942, and by the end of March five 
blimps had been equipped and were in service. 
A total of 14 Mark II units were produced.^'^ 


^ Bell Telephone Laboratories 

The first activity of BTL as already stated 
concerned the two-coil magnetic gradiometer.® 

When it became clear to all involved in this 
development that the methods employed for sta- 
bilizing the magnetometer, as for example in 
the Mark I MAD, were inadequate, develop- 
ment of methods for using the magnetic field 
alone to control the stabilization of the mag- 
netometer were undertaken by several of the 
Section’s contractors. The BTL work resulted 
in the development of a magnetically oriented 
instrument, using saturated-core magnetom- 
eters of the second harmonic type. The BTL 
development of this instrument, known as the 
Mark X MAD, was continued under NDRC 
direction to the stage of laboratory and field 
tests upon a working model. Development and 
design for manufacture of this instrument was 
continued by BTL under a Navy contract with 
the Western Electric Company and by the Naval 
Ordnance Laboratory, and about 50 units were 
produced for possible Service use.®'^® The sys- 
tem was eventually called the AN/ASQ-3.^ 


^ ^ ^ Research Laboratory, General 
Electric Company 

As was mentioned above, the initial program 
of Section C-4 made contractual provision for 
development by the General Electric Company. 

Under the General Electric contract a limited 

^ Field comparisons of AN/ASQ-3 and the AIL type 
AN/ASQ-1 described below are given in references 
17 to 20. 


CONFIDENTIAL 


6 


INTRODUCTION 


consideration was first given to the two-coil 
magnetic gradiometer method.-^ 

The principal effort of the General Electric 
Company related to development of an instru- 
ment to overcome limitations of the Mark 1. 
This employed a magnetometer coil of special 


lar apparatus was terminated before complete 
tests were made.-^ 

The General Electric Company also made an 
exploratory investigation of the possibility of 
employing a rotating “earth inductor” as a 
magnetometer. 



Figure 6. The AN/ASQ-1 magnetic airborne detection equipment. 


design with Permalloy core mounted on an 
electrically driven gyroscope (Figure 4), with 
means for holding the common axis of coil and 
gyro parallel to the earth’s magnetic field. These 
consisted of a pair of Permalloy magnetometers 
perpendicular to each other and to the axis of 
the gyro, the magnetometer outputs being am- 
plified and made to actuate control apparatus. 
For some of the work a d-c amplifier was used 
whose stages consisted of Permalloy saturable 
reactors similar to the magnetometers, instead 
of vacuum tubes. Development of this particu- 


^ Columbia University — Airborne 
Instruments Laboratory 

Development work began under a Columbia 
University contract in June 1941, and after 
about the middle of 1942 practically all MAD 
development work under NDRC direction was 
concentrated in the Airborne Instruments Lab- 
oratory.23-26 During the first year when develop- 
ment was also being undertaken by other groups 
this Columbia group not only carried on experi- 
mental work of its own but also did testing and 


CONFIDENTIAL 


DEVELOPMENT OF MAGNETIC AIRBORNE DETECTOR 


7 


cooperative work for the other groups engaged 
on the same problem. 

Consideration of aircraft operation and ex- 
perience with early MAD models had indicated 
the need for intensive development of methods^"^ 
for stabilizing the magnetometer heads. Devel- 
opment of two methods was for some time con- 
tinued by the Columbia group. 

Gyroscopic Stabilization — 

MAD Mark V 

While magnetically stabilized equipments 
referred to later were being studied and de- 



veloped, further research was carried out on 
gyroscopically stabilized magnetometer heads.^® 
This research resulted in the development of 
an equipment designated MAD Mark V. The 
method employed was in large part that sug- 
gested by A. W. Hull of the General Electric 
Company, and the experimental development 
was carried out by the Sperry Gyroscope Com- 
pany under contract with Columbia University. 

As to the apparatus elements employed, a 
square-head magnetometer group, similar to 
those employed in the MAD I and Mark II, was 
mounted with a modified gyro horizon in a two- 
axis gimbal system so arranged that the de- 
tector magnetometer axis was maintained par- 


allel to the spin axis of the gyroscope. (Figure 
5.) The outputs of the two orientor magnetom- 
eters were used to control the exhaust jets of 
the gyroscope, thereby determining the orienta- 
tion of its spin axis and thus the position of 
the detector magnetometer. This equipment was 
tested in September 1942, and although it was 
ultimately perfected so that its performance 
matched that of the equipment in production it 
was considered not to be well adapted for quan- 
tity production and further development was 
dropped. 

Magnetic Stabilization 

The MAD Mark IV and Mark IV B-1 systems 
and the resulting production models Mark IV 
B-229-33 AN/ASQ-1 (see Figure 6) were 
based on magnetic stabilization of the mag- 
netometer head without the use of any gyro- 
scope. Figure 7 illustrates the principle sche- 
matically. The magnetometers 1-1, connected 
as a pair in a bridge circuit for greater sensi- 
tivity, are arranged to produce a signal when- 
ever there exists a component of H parallel to 
their lengths. The signal voltage is fed to an 
amplifier-modulator which drives a servo motor 
connected to shaft 1. The sense of the resulting 
rotation is arranged to be such as to reduce the 
field component along the magnetometers to 
zero. Magnetometers 1-1 in this manner con- 
tinuously counteract any rotations of the air- 
plane and maintain themselves always perpen- 
dicular to H. Similarly the magnetometers 
2-2, through an amplifier-modulator, actuate a 
servo geared to shaft 2 so as to maintain them- 
selves perpendicular to H. The detecting mag- 
netometers, D-D, being supported normal to the 
plane of 1-1 and 2-2, are therefore maintained 
parallel to H despite the motion of the airplane. 

Further System Improvements 

As a result of research on all the system 
components the AN/ASQ-IA production model 
included the following improvements. 

1. A very steady voltage regulator of the cath- 
ode-loaded type for supplying power to the 
system. 

2. A highly stable bridge-type driver-oscilla- 


CONFIDENTIAL 


8 


INTRODUCTION 


tor for the magnetometers employing a silicon 
carbide varistor as the stabilizing element. 

3. Use of sine wave voltage of a single fre- 
quency for driving all the magnetometers in- 
stead of the previous pulse system, 3“* which was 
noisy. 

4. Biasing methods for precise electrical bal- 
ancing of the four orientor magnetometers. 

5. A lightweight motor system for the mag- 
netometer head servos. 

6. A universal magnetometer head whose 
suspension system permits its use in the 
equatorial regions of small magnetic dip — dur- 
ing maneuvers of the airplane in these areas the 
leads to the magnetometers will become tangled 
if the simple suspension of Figure 7 is used. 

Considerable progress was also made in re- 
ducing the weight of the system and making it 
more compact, especially the magnetometer 
head assembly. Although 270 copies of Mark 
IV B-2 were installed in aircraft during the 
war, it is chiefly the later model AN/ASQ-1 
and its variations which will be described in 
this volume. 



Figure 8. Towed bird arrangement of MAD in- 
stallation. 


During October and November 1942, audible 
signal generators for attracting the attention 
of MAD operators were investigated. These 
devices included means of producing a tone the 
pitch of which varied with the amplitude of the 
MAD signal. The project was discontinued be- 
cause it was found that the operators tended to 
rely upon the sound signal to the total exclusion 


of the more reliable signals provided by the 
recording milliammeter. 

Combating Magnetic Noise 

The limit of sensitivity of the MAD system 
in use is set by the level of magnetic noise pre- 
vailing. As will be discussed more fully in later 
chapters, the two greatest sources of such noise 
are (1) the small-scale hysteresis effects in 
the magnetometer cores and (2) the variable 
fields arising from magnetized portions of the 
airplane or metal parts in which eddy currents 
are induced by the airplane's maneuvers. 



Figure 9. AN/ASQ-1 magnetometer and servo 
assembly attached to wing tip by means of a 
fairing. 

The magnetic core noise was reduced, though 
not eliminated, by very careful handling and 
strain-free mounting of the Permalloy strips 
for the cores. The maneuver noise was reduced 
by two approaches in different systems. In one, 
the towed bird system, the complete magne- 
tometer head assembly was placed in a non- 
magnetic housing towed by a cable sufficiently 
far behind the airplane to be free from its mag- 
netic perturbations, as shown in Figure 8. The 
other scheme was to mount the sensitive head 
on the wing tip or tail, as far as possible from 
most of the metal in the plane, and then to 
install compensating devices in such positions 
as were found by experiment to cancel the 
magnetic fields of the airplane (see Figure 9). 
Chapter 6 describes these methods in detail. 


CONFIDENTIAL 


DEVELOPMENT OF MAGNETIC AIRBORNE DETECTOR 


9 



Figure 10. Equipment developed and produced at Airborne Instrument Laboratory. 


CONFIDENTIAL 


10 


INTRODUCTION 


MAD AUTOMATIC BOMB CONTROL 

In the late summer of 1942, it was decided 
to investigate MAD equipment at AIL in con- 
nection with retro-fired projectiles for vertical 
bombing. This necessitated changes in the pass- 
band characteristics of the Mark IV B-2 in 
order to reduce the time between the passage 
of the aircraft over the target and the produc- 
tion of a peak signal. At about the same time, 
it was proposed to provide means for utilizing 
the output signal from an MAD equipment for 
the automatic release of projectiles. A tripper 
triggered by the signal was to complete appro- 
priate firing circuits after a time delay so that 
the retro-fired projectiles would be released di- 
rectly above the target. 

Late in August 1942, an earlier idea was re- 
vived which proposed using two separate MAD 
equipments to obtain the relative lateral posi- 
tions of the aircraft and the object. For this 
purpose two magnetometer heads were to be 
separated laterally in the aircraft with the out- 
put signals from the two equipments operating 
a single indicator which would give quantita- 
tive data as to the lateral error made in passing 
over a target. It was now proposed that the 
information obtained from the lateral indicator 
be utilized to limit the operation of a tripper so 
the missiles would be released only when the 
lateral range fell between certain predeter- 
mined limits. This system would require two 
complete MAD equipments in addition to the 
tripper and control units. 

Various lateral-control units based on the 
principle of the right-left indicator described 
above were developed during September and 
October 1942. In these units, the signals from 
magnetometer heads on the two wing tips were 
compared in such a way as to provide informa- 


tion as to the lateral range, and means were 
provided to render a tripper (which operated 
on the sum signal) inoperative whenever the 
lateral range was too great for effective bomb- 
ing. This combination of units formed the first 
magnetic airborne bombing system and was 
flown with a dual installation of MAD equip- 
ments in November 1942. It was intended to 
permit the automatic dropping of bombs when, 
and only when, a signal of requisite strength 
was received and the lateral range was such as 
to give effective results. As a later refinement, 
the tripper was arranged to operate either flare 
circuits alone or bomb and flare circuits to- 
gether, depending upon the information pro- 
vided by the lateral-control devices. In other 
words, any signal above a chosen threshold 
would drop a flare regardless of the lateral 
range, while any signal above the threshold 
which occurred with a favorable lateral range 
caused the release of bombs as well as flares. 

At about the same time, right-left indicators 
were investigated which would give semiquan- 
titative visual indications of the lateral range. 
The complete dual systems were given the 
Service designation AN/ASQ-2. Very little op- 
erational experience with these systems was 
obtained before the end of the war, but there 
was indication that further refinement was 
needed (Figure 10). 

In the succeeding chapters of this volume 
many of the matters referred to in this intro- 
duction will be presented in a detailed manner. 
In addition, other matters such as training of 
MAD operators, nature of magnetic anomaly 
produced by a submarine, and uses of MAD 
for land objects will be discussed. A reference 
list of the principal types of MAD equipment 
made under OSRD contract will be found in the 
glossary. 


CONFIDENTIAL 


Chapter 2 


SATURATED-CORE MAGNETOMETERS 


INTRODUCTION 

T he simplest form of saturated-core magne- 
tometeri is a strip of Permalloy around 
which is wrapped a coil carrying an alternating 
current large enough to saturate the metal dur- 
ing part of each cycle. (Other easily saturable 
materials may be used in place of Permalloy, if 
desired.) As the Permalloy core saturates, the 
self-inductance of the coil changes markedly 
during the cycle. This gives the driving current 
a rather complex wave form. 

Now if an external magnetic field also acts 
on the Permalloy a different value of the cur- 
rent in the coil will cause saturation. This will 
change the phases at which the large variations 
in self-inductance occur and so alter the wave 
form of the driving current. If the arrange- 
ment is then connected to a circuit which is 
sensitive to changes in the wave form of the 
driving current it becomes an indicator of the 
magnetic field strength at the position of the 
Permalloy strip. 

This effect has been used in various magne- 
tometers and magnetic compasses for a number 
of years. Figure 1 presents some of the steps 
in the evolution of the saturated-core magne- 
tometer. 

The saturated-core magnetometer does not 
lend itself well to theoretical analysis because 
its operation depends on the nonlinearity of the 
magnetization curve, making it impossible to 
solve explicitly the equation for the voltage 
generated in response to the external magnetic 
field. Analysis can promote understanding of 
the physical phenomena involved, but it should 
be emphasized that it cannot be expected to 
determine design parameters with useful pre- 
cision. 

2 2 THEORY OF OPERATION 

^ The Single-Coil Magnetometer 

Let us first consider a single-coil magnetom- 
eter element driven by a strictly sinusoidal 


current source, as in Figure 2. The air core 
inductance of the coil will be considered neg- 
ligible. If the coil with core had no inductance, 
then the voltage drop, across it would be 
purely resistive and so in phase with the ex- 
citing current. Let this be represented by curve 
ACEC'E'A' in Figure 3. If the coil with core 
had an appreciable constant inductance the 
curve of would be of larger amplitude and 
leading the current, such as BDFD'F'B'. 

Now the inductance of a coil with a ferro- 
magnetic core depends upon the magnetization 
of the core, which in turn depends upon the 
instantaneous current in the coil, upon the 
external magnetic field (if any) and upon 
various dimensions of the system which are 
constants for any particular setup. In the ab- 
sence of an external field a typical graph of 
magnetization versus exciting current for a 
Permalloy core will resemble Figure 4A. Satura- 
tion occurs for currents greater than ±1^. It is 
assumed that the amplitude of the driving cur- 
rent is substantially greater than The in- 
ductance of the coil at any instant depends on 
the slope of this graph since 


L = = NA^' 

di di 

Figure 4B shows approximately how the in- 
ductance of the coil with core varies with 
current. 

Referring again to Figure 3, it is evident 
that for values of the current greater than 
the voltage will follow curve A, and for current 
less than required for saturation the voltage 
will shift to curve B. This shift will not be in- 
stantaneous because of the curvature of the 
magnetization curve, and it will be slower com- 
ing out of saturation than going into satura- 
tion. Consequently, the voltage across Li will 
have a wave form something like curve 
ACDFEC’D'F'E'A'. 

The exact shape of this curve is very sensi- 
tive to slight changes in the experimental con- 


CONFIDENTIAL 


II 


12 


SATURATED-CORE MAGNETOMETERS 


EVOLUTION OF THE SATURATED-CORE MAGNETOMETER 




H ANTRANIKIAN USP 2,047,609 
APP'D AUG 25,1933 



FILED MARCH 27,1935 



GUSTAV BARTH USP 2,252,059 
FILED DEC 24, 1937 
COMPENSATION BY D C 



QnOQQOQQQOQQQ A 




THYRATRON DRIVE \ AMPLIFIER 


UOO UUOUC 



3 WINDINGS -ONE FOR COMPENSATION 
KEY OR BUZZER DRIVE 








AMPLIFIER 



MAGNETOMETERS USED BY AIL 

Figure 1. Evolution of the saturated-core magnetometer. 


CONFIDENTIAL 



THEORY OF OPERATION 


13 


ditions. For example, let us apply a small ex- 
ternal magnetic field parallel to the axis of the 
core. The magnetization curve, as shown in 
Figure 4C, will be shifted slightly to the right 
or to the left, depending on the direction of the 


core will also saturate earlier than for the no- 
field case, causing point E of Figure 3 to occur 
farther to the left. The whole induced voltage 
section CDFE will thus occur earlier in the 
cycle. Similar considerations show that the ex- 




Figure 2. Schematic diagram of single-coil mag- Figure 3. Voltage across single-coil magnetom- 

netometer element. eter element. 


field. Suppose it is shifted to the right. As the 
current decreases from its positive maximum 
the core will begin to desaturate earlier than 






Figure 4. Hysteresis characteristics of saturable 
core elements. 

for the symmetrical no-field case. This will move 
the point C in Figure 3 toward the left. As the 
current approaches its negative maximum the 


ternal field will cause the section C'D'F'E' to 
move to the right in Figure 3. The result is 
shown in Figure 5A. 

If the voltage drop across the magnetometer 
is fed to a circuit which will respond to these 
shifts in the induced voltage pulses, the system 
becomes a sensitive detector for small magnetic 
fields. Subtracting the no-field curve from the 
with-field curve gives the change in output due 
to the field. Figure 5B. The height of these 



I A 

o 
> 

B 

Figure 5. Effect of external field on single-coil 
magnetometer voltage. 

difference-voltage “spikes’" is dependent on the 
magnitude of the external field component par- 
allel to the axis of the core of this single-coil 
magnetometer. An approximate equation for 
the sensitivity will be derived in Section 2.2.4. 
It will be noted that the curve of Figure 5B 
contains only even harmonics of the driving 
frequency. Of these the second is probably 



CONFIDENTIAL 


SATURATED-CORE MAGNETOMETERS 



6 6 
OUTPUT 

Figure 6. DT-l/ASQ-1, detector element sche- 
matic circuit diagram. 


.kAAAt" 



9 — > 


6 6 

Figure 7. DT-l/ASQ-1, orientor element sche- 
matic circuit diagram. 







C 

Figure 8. A. Voltage drop across unequal mag- 
netometers. B. Spike pattern due to bridge un- 
balance, with no external field. C. Output from 
unbalanced bridge with external field. 


ZERORELD SSoMALY ZERO FIELD 

i ♦ * 



TIME— ^ 

Figure 9. Output of magnetometer detector 
bridge when crossing a magnetic anomaly (sche- 
matic) . 



Figure 10. Variation of magnetometer sensitiv- 
ity with dimensions of core strip. 


strongest but the sharpness of the spike gives 
rise to many high harmonics also. 

Although a single-coil magnetometer may 



Figure 11. Variation of magnetometer signal- 
to-magnetic-noise ratio with dimensions of core 
strip. 


serve for the detecting element as just de- 
scribed, greater sensitivity may be obtained by 
using a pair of such elements. These are con- 


CONFIDENTIAL 


THEORY OF OPERATION 


15 


nected in a bridge circuit in such a way as to 
subtract their voltages and only send a spike 
pattern on to the amplifier circuits. The ar- 
rangement is described in the following section. 


MOLYBDENUM PERMALLOY STRIPS 
LENGTH 4.8 INCHES 
THICKNESS 13.6 MILS 
COILS ^8 inch long 
2000 TURNS 


DRIVE FREQUENCY 
• 500 CYCLES 
X200 CYCLES 
□ 100 CYCLES 
O 60 CYCLES 


3 456789 10 20 

^ IN AMPERES PER SECOND 
at 


30 40 5060 60 100 


Figure 12. Sensitivity of magnetometer as a 
function of rate of change of the exciting current. 


2 . 2.2 Magnetometer Bridge' 

Idealized Balanced Bridge 

As shown in Figures 6 and 7 the two coils, 
now assumed identical, may be wound either on 
a single core or on separate parallel cores; 
there is no essential difference in the operation 
of the two varieties. The driving current is sent 
through both coils in series. The voltage ap- 
pearing across the bridge arm is the difference 
between the voltage drops in the two elements. 
If the two elements are identical being 
omitted for this ideal case) and if there is no 
external field, the output voltage will be zero. 

The presence of a small external field will 
spread apart the induced voltage pulses in one 
of the coils in the manner of Figure 5A.* How- 
ever, the other coil is wound oppositely so that 
the magnetization curve of Figure 4C which is 
shifted to the left applies. This causes the in- 
duced voltage pulses to come closer together 
for this coil. The output resulting from the 
bridge subtraction is a spike pattern of twice 
the previous height (for this ideal case). 

Effect of Bridge Unbalances-^ 


to find a perfectly balanced center tap on the 
drive transformer, so that the bridge will not 
usually give absolutely zero output in the ab- 
sence of external field. It turns out to be con- 
venient in designing the detector a .d orientor 
circuits discussed subsequently to have a little 
unbalance in the bridge anyway. A resistor is 
therefore shunted across one of the coils, as 
shown in Figures 6 and 7, to permit adjust- 
ment of the unbalance to the optimum value. 

If the current in is, for example, 99 per 
cent of the current in Lo at any instant, then in 
every cycle the core of will saturate later and 
desaturate earlier than the core of L.^. This 
process will cause the induced voltage pulses in 
Li to be broader than those in Lo, as illustrated 
in Figure 8A. When the two voltages are sub- 
tracted by the bridge circuit the output, even 
with no external field, will be a set of spikes, as 
in Figure 8B. However, this time they are of 
alternating polarity (their analysis contains 
only odd harmonics of the drive frequency). 

When an external magnetic field is applied to 



Figure 13. Variation of B with current for 
magnetometer core strips of different thicknesses 
(showing energy loss due to eddy currents). 


this system the effect is to add the spikes caused 
by the field (Figure 5B) to the spikes caused 
by the unbalance. The result is a set of alternat- 
ing spikes of unequal intensity, illustrated by 
Figure 8C. 


Operation of the Magnetometers 
in MAD 


It is practically impossible to construct two 
magnetometer elements absolutely identical or 


To sum up the previous discussion: the out- 
put of the magnetometer bridge in production 


CONFIDENTIAL 



16 


SATURATED-CORE MAGNETOMETERS 


AIL-MAD equipment is a series of sharp voltage 
pulses (spikes) of alternating polarity and 
equal intensity in the absence of a component 
of external magnetic field parallel to the axis 
of the Permalloy strips. The presence of a 
small component of external field parallel to the 
cores causes the alternate spikes to be of un- 
equal intensity (see Figure 9). The difference 
in magnitude between the plus and minus 
spikes is a measure of the magnitude of the 
field. The positive spikes are larger for one 



.3 .4 .5 .6.7.8 I 2 345678 10 

COIL LENGTH IN INCHES 


Figure 14. Relation between magnetometer sen- 
sitivity and coil length for various core lengths. 


direction of the field component, while the nega- 
tive spikes are larger for the other direction 
of the field component. 

For the two magnetometer pairs which sta- 
bilize the head, as explained in Chapter 1, the 
usual orientation of the cores is normal to the 
ambient field. Any departure from this posi- 
tion due to plane maneuvers causes inequality 
in alternate spike heights which actuates the 
servo system. The magnetometer pair used as 
a detector is maintained by this orienting sys- 
tem parallel to the earth’s field. The steady 
field of the earth is cancelled out by an adjust- 
able direct current from the battery circuit 


shown in Figure 6, so as to leave the detector 
magnetometer sensitive only to a superimposed 
transient field, as from a submarine anomaly. 

Throughout the above discussion a sinusoidal 
current drive has been assumed. It is more 
convenient in practice to use an approximately 
sinusoidal voltage drive. In this arrangement, 
as the inductance of the coil drops upon satura- 
tion more current is drawn from the source, 
which causes a larger voltage drop across the 
internal impedance of the generator. The result 
is a drop in measured voltage across the coil as 
it saturates just as in the current-drive case. 
Therefore the spike patterns will be the same 
as those already considered. 


Sensitivity Formulas®’^ 

The differential equation for the voltage gen- 
erated in a single coil will now be set up. 

Consider the magnetometer coil as a solenoid 
of the same length as the core, whose magnetic 
induction is given by the function B(H). In 
appropriate units the voltage generated across 
one coil of unit cross section is 


or 


dBdH dHi 
^ ~ ” dff dHi dt ’ 


( 1 ) 


where is the value of the applied field due to 
a current i in the coil, and H is a function of 
of the demagnetization factor, and of an ex- 
ternally applied uniform field of small mag- 
nitude. Differentiating with respect to we 
obtain to a first order approximation 



d^B dH dH dHi 
dU^dHidHe dt 


^ _ 9 _ (dH \dHi 1 
dHdHe\dHiJdt r^' 


( 2 ) 


However, since and are both uniform 
fields and affect H in the same way, we have 


dH ^ dH 
dHi dHe 

_9_ ^ 

dHe \dHiJ dHi^ 


CONFIDENTIAL 


MAGNETOMETER DESIGN FACTORS 


17 


In this case we have 



^ aw 1 ^ 
dHdHiU dt 


(3) 


To evaluate consider that, in a uni- 

form field only^ the field H within a needle- 
like strip of ferromagnetic metal is given by the 
equation 


H = Hi- NI, (4) 

where I is the intensity of magnetization and N 
the demagnetizing factor, which depends upon 
the size and shape of the strip. Since B — H 
+ Aul and H is small compared to /, we can 
substitute B — 4jt/ in equation (4) and writing 
k for N/4jr, we have 

II = Hi - kB{H). 

On differentiation we find 


a^ 

dHi 


I k ^ 
^ ^ d// 


(5) 


By using the last expression in equation (3) 
we find 


d^BdHi^^ 



( 6 ) 


For a long solenoid, is proportional to n/l, 
the number of turns per unit length, and to the 
current i. In this case we can write 


AF = dW di 

~ I dm Jt 



(7) 


This is essentially the equation of the spike 
curve of Figure 5B. The result should be 
doubled for a two-coil magnetometer. 

For a given H^, the maximum generated volt- 
age occurs when the product (d^B/dm) (di/dt) is 
maximum. This means that the core should come 
into saturation while di/dt is still large, i.e., to 
achieve maximum sensitivity the cores have to 
be driven well beyond saturation. Beyond this, 
further increase in the amplitude of the exci- 
tation will not materially alter the height of 
the voltage spikes. Equation (7) also indicates 
that, except for the effect of eddy currents, the 
magnetic sensitivity should be linearly propor- 


tional to frequency. These deductions are con- 
firmed by experiment. 

Equation (7) has been derived for a coil of 
the same length as the core, whereas in the AIL 
magnetometers the coils were % inch long and 
the cores were 5 inches long for the detector 
magnetometers and 3.5 inches for the orienting 
magnetometers. It can be seen from equation 
(7) that for a given number of turns n, we 
should expect a greater sensitivity from the con- 
centrated coils than from a distributed wind- 
ing, because the length of the coil I appears 
in the denominator. The rate of change of flux 
in the portions of the strip protruding from 
the coil does not contribute to the generated 
voltage because these portions reach saturation 
some time after the material within the coil is 
saturated, although the protruding ends of the 
core do increase the effective permeability of 
the strip by decreasing its demagnetization 
factor. If, however, the factor n^/l is kept con- 
stant the sensitivity increases with coil length, 
because more of the magnetic material reaches 
saturation at the same time, thus sharpening 
the curvature of the hysteresis curve at the 
point of saturation. In other words, the maxi- 
mum value of d'^B/dm is increased. 

Presumably it should be possible to construct 
the voltage-time graph for the magnetometer 
by computing the terms entering into equation 
(7) point by point from the B-H curve and 
other data or even more directly by accurately 
measuring the voltage contribution of each coil 
and the phase shifts produced by the applica- 
tion of the external field. This graphical analysis 
has yielded qualitative results in agreement 
with experiment.® 


2 ® MAGNETOMETER DESIGN FACTORS 

The design factors^- entering into the con- 
struction of the magnetometers can be listed as 
follows. 

1. The core material. 

2. The cross-sectional area of the core. 

3. The ratio of the core length to its cross- 
sectional area. 

4. The B-H curve of the core. 

5. The design of the coils. 


CONFIDENTIAL 


18 


SATURATED-CORE MAGNETOMETERS 


6. The amplitude and the frequency of the 
energizing current. 

7. The extent to which the core is laminated 
for reducing the effect of eddy currents. 

8. Strain-free mounting of the cores. 

Investigation of several core materials re- 
vealed that the nature of the material has a 
bearing on the residual noise of the magnetom- 
eter but has little influence on the sensitivity. 



Figure 15. DT-l/ASQ-1 unit, detector assembly 
showing coils and strip. 

The results of this investigation at AIL are 
summarized in Table 1. 

The experimental curves in Figures 10 to 14 
are reproduced to indicate values of the design 
factors. They are for cores consisting of a single 
strip of material. Unless specified, the cores are 
Vs inch wide ; the coils, 2,000 turns layer wound 
with No. 40 wire, % inch long; the frequency 
of the drive, 400 c. 

2-^ MAGNETIC CORE NOISEii ^^ 

It is believed that the sensitivity of saturated- 
core magnetometers is limited by the failure 


of the core material to repeat exactly its mag- 
netization curve from cycle to cycle. The in- 
fluence of the nature of the material on the 
signal-to-noise ratio was given in Table 1. If 


Table 1. Sensitivity-noise ratio for various met- 
als as used in saturable magnetometer cores. (The 
units are arbitrary.) 


Metal 

Sensi- 

tivity 

Noise 

Sensi- 

tivity/ 

noise 

4-79 Permalloy 

4-4. 8-15 

50 

10 

5 

5-4. 8-14 

50 

9 

5 . 6 

6-4. 8-14 

50 

10 

5 

7-4. 8-14 

49 

10 

4 9 

High-mu Permalloy 

12-4. 8-14 

62 

22 

2.8 

Mumetal, M-4. 8-15 

65 . 6 

27 

2.4 

No. 143 Alloy, A-5-10 

41 

58 

0.7 

Perminvar, V-5-10 

39 

354 

0.1 


I 



Figure 16. DT-l/ASQ-1, bottom view of Mycalex 
plate showing orientor element strips and coils. 


the variations of magnetization can be attrib- 
uted to Barkhausen discontinuities, then for 
a given material it is reasonable to expect some 
improvement from increasing the cross-sec- 
tional area of the core. This was done by BTL 
without increasing eddy current losses by 
rolling a sheet of Permalloy 0.001 inch thick 


CONFIDENTIAL 



MAGNETIC CORE NOISE 


19 


into a scroll-shaped core. Smaller variations in 
magnetization from cycle to cycle can be also 
expected from a magnetometer in which the 
core or cores are magnetized by solenoids at 
least as long as the cores, so that all the ma- 
terial is brought to saturation at the same time, 
and by increasing the amplitude of the driving 
current. These expectations have been verified 
by experiment. 

For the standard AIL magnetometers in 
AN/ASQ equipment the value of magnetic 
noise level is of the order of 0.2 gamma. In the 
case of special experimental second-harmonic- 
type detectors, the smallest noise level reported 
was 0.03 gamma. 


In order to achieve this low level of magnetic 
noise, constraint of the core material must be 
specially avoided. Any supports which cause 
bending or tension of the core strips result in 
increased noise. In the AN/ASQ-1 equipment 
the strips and coils of the magnetometer ele- 
ments are supported in a wax of sufficiently 
high melting point as to prevent appreciable 
flow at the operating temperature. For further 
protection the whole is then enclosed in a glass 
tube. Figure 15 shows a detector element as- 
sembly, and Figure 16 shows the manner of 
mounting the orientor elements. References 14 
to 18 describe the techniques used in selecting, 
matching, and mounting the elements. 


CONFIDENTIAL 


Chapter 3 

THE AN/ASQ-1 DETECTION EQUIPMENT 


3 1 GENERAL DESIGN CONSIDERATIONS 

T he purpose of the AN/ASQ-1 system was 
the employment of a saturated-core mag- 
netometer for the detection of submerged sub- 
marines from aircraft. This was accomplished 
by the detection of the local anomaly produced 
in the earth's magnetic field by the presence of 
the submarine. The range at which the sub- 
marine could be so detected is a function of 
the minimum observable anomaly. The size of 
this limiting anomaly or “signal" is in turn 
dependent upon the magnetic moment of the 
submarine and the level of all the various un- 
wanted fluctuations, magnetic, electrical, or 
mechanical in origin, which appear on the in- 
dicator of the system. 


^ Character of the Submarine 
Anomaly 

For the purpose of approximating the way 
in which the strength of the anomaly field de- 
pends upon distance from the submarine, this 
field may be considered to be produced by a 
simple dipole source. To this degree of ap- 
proximation the field varies as the inverse cube 
of the distance from the source. The value of 
the equivalent magnetic moment of a submarine 
depends upon its size, its magnetic heading, its 
magnetic latitude, and the state of its per- 
manent magnetization as influenced by its 
previous history. The actual values of magnetic 
moments of submarines which were measured 
during the war varied from 1 X 10^ cgs units 
to about 30 X 10^ cgs units.^ Thus, the order 
of magnitude of the magnetic anomaly at a 
distance of 400 feet from a representative sub- 
marine would be 10 gammas.’' 

The average value of the earth’s field, in, say, 

^ It should be noted that these moments might pos- 
sibly be reduced by a factor of 10 by careful degaussing 
of the submarine. However, to be effective at all times 
the degaussing equipment would have to be carried on 
the submarine and kept in continuous operation. 

One gamma equals lO'^ oersted. 


the North Atlantic region is approximately 
60,000 gammas. Bearing in mind that anomalies 
considerably smaller than the example quoted 
above must be detectable for the system to be 
successful, it is clear that the first requirement 
on the system is that it be capable of detecting 
and indicating an anomaly in a vector field 
whose size is approximately one part in 60,000 
of the ambient value of that field. 

At any point the resultant field is the vector 
sum of a constant field due to the earth and the 
small field due to the submarine. Even if the 
latter is at right angles to the earth’s field it 
will not change the direction of the resultant 
vector more than about arctan 10/60,000 or 30 
seconds of angle. Since the orienting mechanism 
will not respond to such a small variation, the 
detecting magnetometer will retain the same 
direction it had before approaching the sub- 
marine. Therefore that feature of the anomaly 
which will be impressed upon the detector at 
any point is essentially its component in the 
direction of the earth’s field. The magnitude 
and variation of the magnitude with position 
to be expected of this quantity can be worked 
out mathematically^-^ or measured with models 
in the laboratory, assuming the submarine to 
be equivalent to a magnetic dipole. Figure 1 
shows a contour map obtained from model ex- 
periments in the manner to be described in 
Chapter 4. The submarine was assumed to 
have a magnetic moment of about 15 X 10^ cgs 
units so oriented as to lead to those longitudinal, 
transverse, and vertical components of its 
moment listed in the figure. By laying a rule 
across such a contour map one may plot the 
field which must be detected by the magnetom- 
eter during any straight flight of the airplane 
over this submarine at 200 feet vertical separa- 
tion. Figure 2 shows such a plot on another 
model contour map. 

Since the aircraft which carries the AN/ 
ASQ-1 equipment flies through the anomaly 
field of the submarine, the detection of the 
anomaly is a dynamic phenomenon. Figures 3 
and 4, which are plotted on a time axis, show 


20 


CONFIDENTIAL 


GENERAL DESIGN CONSIDERATIONS 


21 


the results to be expected in crossing the con- 
tours of Figure 1 at 100 knots. The anomaly 
signal is a transient disturbance to the energy 
of which a frequency distribution may be as- 


craft speed of 120 knots and distance of closest 
approach of submarine 400 feet, this band ex- 
tends roughly from 0.01 c to 10 c. Therefore, 
in attacking the problem of maximizing the 


(00 ' 


MAG N 


.-2r 


/ 

/ 


/ 


/ 


\ 

\ 



My=5xl0^cgs DOWN 
DIP =50 DEGREES 
S=HEADING = 135 DEGREES 
VERTICAL SEPARATION = 200 FEET 


Figure 1. Static contour map, showing magnitude of component parallel to earth’s field at 200-foot level 
of the magnetic anomaly due to a typical submarine model. 


signed. The frequency band in which most of 
this energy lies is determined by the extent of 
the anomaly and the speed of the aircraft. 
Under typical operational conditions, e.g., air- 


ratio of signal to undesired background fluctua- 
tions or “noise,” only that noise which lies in the 
above-mentioned frequency band need be con- 
sidered. 


CONFIDENTIAL 


22 


THE AN/ASQ-1 DETECTION EQUIPMENT 


Noise Reduction 

The background noise, ^ which limits the 
range at which a submarine may be detected, 
may be classified into five different types as 
follows: (1) natural fiuctuations with time in 
the terrestrial magnetic field, (2) fluctuations 
in the output signal of the magnetometer aris- 
ing from rotation of the axis of the magnetom- 
eter with respect to the direction of the terres- 



Figure 2. Model static contour map, with plot of 
field strengths encountered by a plane on a level 
45° course passing over the submarine at 200- 
foot vertical separation. (N-S arrow 200 feet 
long in center of chart represents submarine.) 

trial field, (3) magnetic fluctuations caused by 
magnetic sources close to the detection equip- 
ment, (4) random fluctuations in the output 
signal of the magnetometer generated in the 
process of carrying the magnetometer core 
material through successive hysteresis loops, 
so-called core noise, (5) fluctuations in the in- 
dicating system introduced by microphonics, 
fluctuations in power supply voltage, etc. A 


spurious signal will also occur when passing 
over an anomaly in the earth’s field of geologi- 
cal origin. 

1. Terrestrial magnetic noise is beyond the 
control of the design engineer. Fortunately, 
it is extremely small at these frequencies except 
during intense magnetic storms or in the imme- 
diate neighborhood of a thunderstorm, as indi- 
cated in Chapter 7. The other types are suscep- 
tible to reduction by means of improved design. 

2. In order to control fluctuations due to 
magnetometer motion successfully, the paral- 
lelism of the magnetometer axis and the di- 
rection of the ambient field must be maintained 
to five minutes of arc. A variation of this 
amount in angle will produce an apparent 
change, in the magnetic field as measured by 
the magnetometer, of 0.06 gamma, which is 
adjudged to be the maximum tolerable noise 
from this source. The complete electromechani- 
cal servo system must have suitable dynamic 
characteristics; that is, it must not oscillate 
of itself, it must have the proper internal damp- 
ing, yet it must be sufficiently rapid in its 
response to accommodate the angular motions 
required by the maneuvers of the carrying 
aircraft.®’ One feature of the stabilizing mech- 
anism, which is of vital significance, should 
be noted at this point. Since the two stabilizing 
magnetometers are normally perpendicular to 
the direction of the earth’s field, they have a 
maximum sensitivity to rotations of the mag- 
netometer array. This is in contrast to the 
signal detector, whose sensitivity to such rota- 
tion is at a minimum, because the cosine is a 
slowly varying function near zero degrees. 
Therefore, for magnetometers of the same 
sensitivity to change in field parallel to their 
respective axes, the voltage output of the 
stabilizing magnetometers for a given error 
in alignment is many times the output of the 
signal-detector magnetometer due to this error. 
It is this differential in sensitivity to orienta- 
tion error which permits the above-described 
principle of stabilization to be used. Orientation 
of the detector exactly parallel to the magnetic 
vector, rather than at some slight but equally 
well maintained angle, is most important. For 
the detector parallel to the magnetic axis, a 
deviation of 1 degree decreases the measured 


CONFIDENTIAL 


GENERAL DESIGN CONSIDERATIONS 


23 


field only 9 gammas, whereas if it were 3 de- 
grees from parallel, an additional degree would 
decrease the field about 60 gammas. Since the 
necessary accuracy of construction of the mag- 
netometer head is too difficult to attain readily, 
small neutralizing currents are sent through 
the orientor magnetometers of AN/ASQ-1. 
These are adjusted by trial until the orientors 



Figure 3. Signal resulting from crossing the 
contours of Figure 1 at 100 knots. 


give zero output when the detector is strictly 
parallel to the field.® 

3. Let us now take up noise produced by local 
sources of magnetism. For convenience these 
may be broken into two classes: those sources 
which are part of the magnetometer and servo 
mechanism assembly, and those sources which 
are associated directly with the carrying air- 
craft. In the design and construction of the 
magnetometer head, that is, the servo motor 


and magnetometer array assembly, every care 
must be taken to insure that ferromagnetic 
materials are absent or at least sufficiently re- 
mote from the magnetometer assembly so as 
not to cause serious noise. There remains the 
transient magnetic field associated with eddy 
currents induced in nonferromagnetic conduc- 
tors, which of necessity are in some cases very 



Figure 4. Signal resulting from crossing the con- 
tours of Figure 1 at 100 knots. 


close to the magnetometer array, such as metal- 
lic parts of the gimbal system. These parts 
must be so designed as to avoid large sheets or 
closed loops which would permit flow of cur- 
rents induced by motion in the earth’s field. 
The procedure for dealing with sources of 
magnetism associated with the aircraft is dis- 
cussed in Chapter 6. 

4. Noise generated in the core material it- 
self is one of the more fundamental types of 


CONFIDENTIAL 


24 


THE AN/ASQ-1 DETECTION EQUIPMENT 


noise and may be the ultimate limitation to the 
sensitivity of a saturable-core magnetometer. 
This has been discussed in Chapter 2. 

5. Noise arising from the electronic part of 
the system, that is, vacuum tube microphonics, ^ 



Figure 5. The DT-l/ASQ-1 polar magnetometer 
head and servo motor assembly used in the 
AN/ASQ-1. 

fluctuations in the signals caused by erratic 
power supply voltages and similar phenomena, 
may be dealt with by conventional or semicon- 
ventional electronic engineering practice. In 
some cases special circuit details were incor- 
porated in AN/ASQ-1, and in others drastic 
requirements in regard to production, inspec- 
tion, and tube selection were imposed in order 
to minimize this source of noise. In the fin- 
ished circuit, noise due to the detector, ampli- 
fier, and driver was measured as about 7 per 
cent of the total internal noise and was there- 
fore negligible. 

The principal design effort was directed to- 
ward the reduction of the classes of noise just 
discussed. There are, however, other considera- 


tions which limit the form which the system 
can take. Since the equipment must be air- 
borne the usual limitations of size and weight 
apply. This was especially important for the 
AN/ASQ-1, since it was intended to install two 
complete systems in many aircraft for auto- 
matic bombing, as described in Chapter 4. In 
addition, on account of the need for dealing 
with noise arising from local sources of mag- 
netism in the aircraft, restrictions are placed 
on the location of the magnetometer head. This 
condition imposes even more stringent limita- 
tions on the size and shape of this part of the 
system. Another condition is imposed by reason 



Figure 6. The DT-l/ASQ-1 polar magnetometer 
head used in AN/ASQ-1. 


of the transient nature of the anomaly signal. 
It was early noticed that the effective signal- 
to-noise ratio was increased when a continuous 
record of the magnetometer indications was 
used. Since the anomaly signal was not repeti- 


CONFIDENTIAL 


DESCRIPTION OF SYSTEM OPERATION 


25 


live the memory feature of a continuous record 
greatly aids the observer’s eye in distinguishing 
a small anomaly signal from spurious back- 
ground fluctuations. 


AIRCRAFT 



Figure 7. Schematic functional diagram of 
AN/ASQ-1. 


» 2 DESCRIPTION OF SYSTEM 

OPERATION 

A photograph of the AN/ASQ-1^®’ equip- 
ment was shown in Figure 6 of Chapter 1. It 
occupies 3.9 cubic feet of space and has a normal 
installed weight of 135 pounds including in- 
stallation accessories. Figure 5 shows the 
magnetometer and servo motor assembly re- 
moved from its housing. This assembly and 
housing were installed in various locations on 
different types of aircraft, as will be discussed 
in Chapter 6. Figure 6 is a close-up view of the 
square-head magnetometer assembly. This is 
the DT-l/ASQ-1, or ‘'polar head.” The arrange- 
ment of the three magnetometer pairs is as 
sketched in Figure 7 of Chapter 1. 

A schematic functional diagram of the vari- 
ous parts of AN/ASQ-1 is given in Figure 7. 



Figure 8. Location of AN/ASQ-1 circuit sections. 


The fundamental power supply is the 24-volt 
The fundamental engineering design features d-c system of the aircraft, from which this 
utilized to meet the conditions laid down in the equipment draws 8 to 12 amperes. This cur- 
foregoing paragraphs are discussed in the next rent operates a dynamotor producing about 
sections. 550 volts direct current which, when passed 


CONFIDENTIAL 



26 


THE AN/ASQ-1 DETECTION EQUIPMENT 


through a filter and an electronic voltage regu- 
lator, serves to operate a 400-cycle master oscil- 
lator. The 400-cycle voltage is fed to the detector 


cuit which will be described more fully in 
Section 3.4.2. If the spikes are of equal height 
the output of the amplifier is zero, but in the 


F-303 


R-301 
0.05 K 

HWVi 

L-301 


n M6-30. S 4’"°" J 

>-^ I ' 2 ^ 

f ^ 

0,005 I 

11^, _I_C-306 

11"^ ~^O.OlMf 


o L-302 


.C-303 
4 /if 


C-305 
0.00 5>if 


C-301 

0.005/if 


T) F-301 


C-307 

I/It 


F-302 


Q GROUND 

© 

-@FROM AIRCRAFT BATTERY +24 V 


®{i 

i®, 

©: 


TO RECORDER LIGHT 
TO TERMINAL I OF 0-|/ASQ'l 
TO TERMINAL I OF AM-I/ASQ-I 

TO COMMON GROUND POINT 
IN JUNCTION BOX 


TO RECORDER LIGHT 
TO TERMINAL 2 OF 0-l/ASQ-l 
TO TERMINAL 2 OF AM-I/ASQ-I 

® T0 COMMON GROUND POINT 
IN JUNCTION BOX 

-(T)tO TERMINAL 15 OF 0-l/ASQ-l 

-(f) FROM TERMINAL 16 OF AM-I/ASQ-I 

_{g)T0 terminal 16 OF 0-l/ASQ-l 

© 

— (T)tO terminal 28 OF 0-l/ASQ-l 


Figure 9. The DY-4/ASQ-1 dynamotor-filter power supply schematic circuit diagram. 


and stabilizer magnetometer coils through ap- 
propriate driver circuits and also to the field 
windings of the servo motors. 



Figure 10. The DY-4/ASQ-1 dynamotor-filter 
power supply unit. 

The spike pattern output of the detector ele- 
ment bridge goes to the detector-amplifier cir- 


presence of a magnetic anomaly pattern, such 
as shown in Figure 9 of Chapter 2, a low-fre- 
quency transient voltage corresponding ap- 
proximately to the envelope of the spikes is sent 
to the recording milliammeter. The recorder 
therefore traces an approximate graph of the 
time variation of magnetic field component 
parallel to the detector element. An auxiliary 
ammeter is also placed near the pilot’s seat. 
The battery circuit which neutralizes the steady 
field of the earth is included in the detector 
amplifier in this diagram. 

The outputs of the two stabilizer bridges go 
to the two stabilizer amplifier circuits. The 
way in which these control the servo motors 
has not yet been described. The system is as 
follows. The circuits are so arranged that in 
the absence of error-signal from the bridges 
they send 800-cycle voltage to the servo control 
windings. The field windings of these motors 
are continuously receiving 400-cycle voltage 
from the master oscillator. The 800 cycles on 
the control windings therefore produces no 
effect. However, as soon as a motion of the 
aircraft throws the magnetometer head out of 


CONFIDENTIAL 


C-202II ^ . C-201 I I O.I>xf 


DESCRIPTION OF SYSTEM OPERATION 27 



Figure 11. The 0-1/ASQ-l driver unit, schematic circuit diagram. C204 must be adjusted to give a fre- 
quency of 400 c ±1. B+ to be adjusted to 300 v ±2% by selecting proper values of R212 and R213. 


CONFIDENTIAL 


28 


THE AN/ASQ-l DETECTION EQUIPMENT 


correct alignment, the stabilizer elements will 
experience field components parallel to their 
axes. The resulting changes in the spike pattern 
outputs of the bridges are translated by the 



Figure 12. The electronic regulator circuit in 
0-1/ASQ-l. 


stabilizer amplifier circuits into 400-cycle volt- 
ages. Voltages of this frequency will cause the 
servo motors to rotate as long as they persist. 
The phases are properly adjusted to make the 



Figure 14. The detector driving amplifier circuit 
in 0-1/ASQ-l. 


directions of the rotations such as to remove the 
error in magnetometer head alignment. As 
soon as the detector element is once more 
parallel to the field the stabilizer elements will 
be in the no-field position. The resulting pat- 
tern of spikes of equal height is translated 
again into 800-cycle voltage by the amplifier 
and the servos cease operating. 


The stabilizer control circuit shown on the 
diagram includes the neutralizing circuits for 
correcting any lack of perpendicularity between 
detector and stabilizer elements on the head. 



Figure 13. The 400-cycle oscillator circuit in 
0-1/ASQ-l. 


Figure 8 shows the location of the different 
circuits in the cabinet assemblies as manu- 
factured. The next sections will take up the 
operation of these circuits one at a time. 



Figure 15. The orientor driving amplifier circuit 
in 0-1/ASQ-l. 


3 3 the power and driver 

CIRCUITS 

^ The Power Unit, DY4/ASQ-1 

The schematic diagram of the dynamotor- 
filter circuit is given in Figure 9, and a top 
view of the unit is shown in Figure 10. The 


CONFIDENTIAL 


THE POWER AND DRIVER CIRCUITS 


29 


aircraft battery power is applied to the 5,200- 
rpm dynamotor MG301 through a power relay 
and a low-pass filter (L301, R301, C301, and 
C302). This filter prevents dynamotor brush 
noise from causing interference in the rest of 
the aircraft electrical system. The relay is actu- 
ated by the Power switch on the control unit 


C207 R247 



C208 R248 

Figure 16. The constant servo motor field am- 
plifier circuit in 0-1/ASQ-l. 

panel. The high-voltage output of the dyna- 
motor passes through an r-f filter (L302, C304, 
C305) before being sent on to the succeeding 
units of the system. 


3.3.2 Voltage Regulator 

Figure 11 is the schematic circuit diagram 
of the 0-1/ASQ-l driver unit. This assembly 
includes the electronic voltage regulator, the 
400-cycle master oscillator, the driver for the 
detecting magnetometer bridge, the drivers 
for the stabilizing magnetometer bridges, and 
the 400-cycle supply for the field windings 
of the two servo motors. Figure 12 is a detail of 
the regulator circuit alone. 

If the dynamotor voltage increases, the cur- 
rent through the tube V201 becomes greater 
and the grid voltage for control tube V202 is 
increased. This results in a decrease in plate 
voltage on V202 which causes a decrease in the 
output of cathode follower V202', thus lowering 
the grid voltage of the four regulator tubes, 
V203, V204, V205, and V206. The greater 
voltage drop across these tubes compensates 
for the increased input voltage. The system op- 


erates analogously to compensate for decreases 
in voltage. If the aircraft battery power sup- 
ply varies over the range 20 to 30 volts the 
dynamotor output will vary between 450 and 
720, but the regulated output will lie between 

297.2 and 297.8 volts. 


3.3.3 400-Cycle Oscillator 

A detail of the 400-cycle oscillator circuit is 
shown in Figure 13. The oscillator consists of 
a two-stage amplifier, utilizing tubes V207 and 
V208. The tubes’ output is fed back to the input 
in the proper phase to sustain oscillation 
through a coupling transformer T201 and a 
resonant bridge circuit. The center-tapped sec- 
ondary winding of T201 comprises two arms 
of the bridge; iron-core inductor L201, mica 
capacitor C204, and Varistor R244 comprise 
the third, while wire-wound precision resistor 
R223 forms the fourth. The third arm is tuned 



Figure 17. The AM-l/ASQ-1 control unit. 

to give an output of 400c, although phase shifts 
in the feedback circuit cause the output fre- 
quency to differ slightly from the resonant 
frequency of the tank circuit. 

The grid of tube V208 is driven by the 
potential which appears between the grounded 
center-tap of T201 and the junction of the 
third and fourth arms of the bridge. The ampli- 
tude of this driving voltage is determined by 
the ratio of the impedance of the resonant arm 
to the resistance of R223. The resistance of 
Varistor R244 varies inversely with the poten- 


CONFIDENTIAL 


30 


THE AN/ASQ-1 DETECTION EQUIPMENT 


tial difference at its terminals. Its purpose is 
to regulate the voltage across the resonant arm 
of the bridge. Thus, if the voltage across T201 
should rise because of increased output from 


V208 and thus decrease the voltage across 
T201. If the filament-to-plate voltages applied 
to tubes V207 and V208 should decrease, the 
Varistor would operate in the opposite direc- 



tubes V207 and V208 resulting from increased 
filament or plate voltage, the resistance of R244 
would decrease and further shunt the circuit 
of L201 and C204. This would reduce the 
amplitude of the drive voltage to the grid of 


tion. Thus the amplitude of the oscillator out- 
put voltage, tapped off of points 1 and 3 across 
the T201 secondary for use in the later circuits, 
is maintained very nearly constant. 

Cathode resistors R218 and R220 of tubes 


CONFIDENTIAL 




THE POWER AND DRIVER CIRCUITS 


31 


V207 and V208 are not by-passed. The result- 
ing degeneration tends to relieve the require- 
ment for nonmicrophonic tubes and further 
reduces the effect on the oscillator output of 
variations in filament voltage. The filter net- 
work, consisting of R214 and C202, is for the 
purpose of suppressing parasitic oscillations. 


3.3.4 Magnetometer Driving Amplifiers 
and the Motor Field Amplifier 

The output of the oscillator is applied to 
three separate amplifier channels, the secondary 
winding of transformer T201 providing push- 



Figure 19. DT-l/ASQ-l unit, schematic circuit 
diagram. 


respective grids through 1-megohm resistors to 
provide voltage degeneration. This effect re- 
duces the microphonic and d-c voltage varia- 
tions and the harmonic distortion. 



VOLTAGE DROP IN 
V102 CATHODE 
RE SI STOP 




V104 PLATE 
CURRENT 



0 


INPUT SIGNAL 
TO V10I GRID 




VOLTAGE DROP IN 
VI 01 CATHODE 
RESISTOR 




0 


V103 

PLATE CURRENT 



0 


pull drive for all three, as shown by Figures 
14, 15, and 16. 

The detector-magnetometer elements are 
driven by the amplifier channel with tubes V209 
and V210; the orientor elements, by the ampli- 
fier with tubes V211 and V212; and the con- 
stant fields of the motors are energized by the 
amplifier with tubes V213, V213', V214, and 
V215. The input grids of all three channels are 
connected to terminals 1 and 3 of transformer 
T201 through resistors which serve for isola- 
tion. The plates of all the amplifier tubes ex- 
cept V213 and V213' are connected to their 



Figure 20. Schematic graphs of voltage and cur- 
rent variations within the detector amplifier cir- 
cuit (not to scale). 

Capacitor C205 is connected across the 
primary winding of transformer T202 to re- 
duce distortion by tuning the output of the 
detector-driver amplifier channel to 400 c. 
Similarly, capacitor C206 is across the primary 


CONFIDENTIAL 


32 


THE AN/ASQ-l DETECTION EQUIPMENT 


winding of output transformer T203 of the 
orientor-driver to improve the wave form and 
bring the phase angle between the outputs of 
the orientor and motor field channels to zero. 


1.0 



0.01 — — I ' ‘ ‘‘ H I — — I I 1 1 1 1 — — I I N I 

0.01 0.1 1.0 10.0 
FREQUENCY IN C 

Figure 21. Response-frequency characteristic of 
AN/ASQ-l exclusive of recorder. 

In the motor field amplifier circuit, capacitor 
C209 is connected across the secondary of trans- 
former T204. The capacitor is chosen to obtain 
maximum output. This occurs when its com- 
bination with the transformer winding and 
the constant field windings of the servo motors 
has a resonant frequency of 400 c. 


3 » THE DETECTOR CIRCUITS 

The amplifier for the detector bridge output 
and the battery circuit for neutralizing the 
constant effect of the earth’s field are contained 
in the chassis labeled AM-1, /ASQ-1 shown in 
Figure 17. This chassis also contains the orient- 
ing magnetometer circuits to be described in 
Section 3.5. The schematic diagram is given in 
Figure 18. The wiring of the magnetometer 
head and servo motor assembly is shown by 
Figure 19. 


^ ^ ^ The Magnetic Neutralizing Circuit 

The 4.5-volt dry cells BlOl and B102 send 
current in the same direction through both 
coils of the detecting magnetometer so as to 
cause a field throughout the Permalloy strip 
equal and opposite to the constant field of the 


• 

earth. (The field due to the 400-cycle driving 
current is oppositely directed in the two halves 
of the strip, so as to cause the detecting effect 
as previously described.) The rheostats R102 
and R103 which control this neutralizing cur- 
rent appear on either side of the meter in 
Figure 17. 

Switch SW102, in the bottom center of the 
control panel, is a test switch. Closing it in 
either direction causes a small change in the 
neutralizing current and provides the so-called 
click test. The change in current has the same 
effect on the detector element as a change in 



o.ot 0.1 1.0 10.6 


FREQUENCY IN C 

Figure 22. Response-frequency characteristic of 
AN/ASQ-l, including recorder. 

the earth’s field. The click test shows whether 
or not the equipment is operating properly and 
also gives a rough check on its sensitivity.^- 


3.4.2 Detector Amplifier Circuit 

The upper half of Figure 18 is the diagram 
of the signal amplifier. Figure 20 indicates the 
general nature of the signal response at several 
points in the circuit. 

The Amplification Principle 

The voltage between terminals 1 and 2 on 
the secondary of TlOl will repeat the spike 
pattern of the magnetometer bridge output. 


CONFIDENTIAL 


THE DETECTOR CIRCUITS 


33 


V102 will pass current (passing most on the 
positive spikes of the grid signal) until the 
charge in C102 builds up sufficiently to main- 
tain an average negative grid bias of about 50 
volts. The condenser does not discharge com- 
pletely between pulses because the time con- 
stant of the circuit C102-R110 is large compared 
to the pulse period. The voltage across RllO 
traces a sawtooth curve of about 1 volt “tooth- 


VERTICAL HORIZONTAL 



Figure 23. Response of AN/ASQ-1 without re- 
corder, to various magnetic signals of submarine 
type and to a discontinuous change in magnetic 
field. 

height.” When a magnetic anomaly signal 
causes the positive spikes to increase and the 
negative ones to decrease, the result is an in- 
crease in the average current through the 
tube. The average voltage drop across RllO 
increases as shown in Figure 20. 

The potential of the V104 grid therefore 
rises; this tube then passes more current and 
a greater drop across its plate resistor results. 
This lowers the potential of contact 4 on R187 
and so decreases the current through V105. 
The resulting rise in the latter’s plate voltage 
raises the grid potential of V106, increases the 
V106 plate current, and so lowers the potential 
of the point between R134 and R136 which con- 
stitutes one terminal of the output. 


The independent companion channel, con- 
taining tubes VlOl, V103, V105', and V106', is 
likewise a four-stage RC-coupled amplifier. 
Since VlOl is connected in the opposite direc- 
tion across TlOl as compared to V102, a mag- 
netometer bridge spike which decreases the 
grid bias of VlOl increases that of V102 and 
vice versa. A similar opposition in polarity 
continues throughout this amplifier, with the 
result that the potential of the output point 
between R137 and R135 rises at the time the 
potential of the upper channel output point 
falls. The recording milliammeter and remote 
signal meter which are connected in series be- 
tween these two points receive by this mecha- 
nism an amplified voltage pulse of approxi- 
mately the same shape as the magnetic signal. 

Circuit Details 

Any inequality in amplification between the 
first two stages of the upper channel and the 
first two stages of the lower channel may be 
balanced out by a slight alteration of the plate 
voltages of V103 and V104. This is done by 
shorting the driver pulses with switch SWlOl 
and then adjusting the screwdriver control of 
rheostat R186 until the microammeter MlOl 



reads zero. A similar opportunity for balancing 
the circuit as a whole is given by adjustable 
rheostat R188 at the output end. 

The amplification of the circuit may be varied 


CONFIDENTIAL 


34 


THE AN/ASQ-1 DETECTION EQUIPMENT 


by means of the dual potentiometer R187 
located in the center of the control panel. A 
change in the position of its two sliders — 
coupled together and moving oppositely — alters 
the fraction of the V103 and V104 plate voltage 


submarine signals. The lowest frequencies, 
principally caused by magnetic fluctuations 
within the aircraft, are blocked by the con- 
densers in series, such as C106. High-frequency 
transients are shorted out by the condensers 


B+ C*I36 C*I38 



variation which is passed on to the V105 and 
V105' grids. 

The four similar filter networks (C106, C108, 
Clio, Vo R187), (C114, C 116 , C 118 , R128, 


in parallel, such as CllO. Figure 21 gives the 
frequency response of the amplifier alone and 
Figure 22 shows the effect of including the 
mechanical recorder. Figure 23 is a series of 


MAGNETOMETER 
BRIDGE OUTPUT 


PROPER ORIENTATION 


CLOCKWISE TILT ► I * 1 * I * | * | * | * 


COUNTERCLOCKWISE TILT ► * | * | * | * | * | ‘ 


FREQUENCY- DOUBLER 
OUTPUT 

AMPLIFIER 

OUTPUT 

MOTOR 

ACTION 

wmm 

800 C 

VWWWVAAA/ 

STATIONARY 


400 C 

180* PHASE 
DIFFERENCE 

ROTATES 

COUNTERCLOCKWISE 



ROTATES 

CLOCKWISE 


Figure 26. Illustrating directional control of stabilizers. 


R130), (C107, C109, cm, 1/2 R187), and oscillograms showing the output voltage of 
(C115, C117, C119, R129, R131) determine the AN/ASQ-1, without recorder, in response to 
frequency response of the system — placing the some magnetic signal of typical submarine type 
pass band in the range occupied by the usual and also to a discontinuous change in magnetic 


CONFIDENTIAL 



THE ORIENTOR CIRCUITS 


35 


field.13 Resistors R119, R120, R126, and R127 
are added to provide the proper plate loads for 
their respective tubes. 

The feedback condensers C104, C105, C112, 
and Cl 13 help to lower the gain for high-fre- 



Figure 27. Test record made under magnetically 
quiet conditions. 


quency signals. The feedback currents flow 
through the adjoining grid resistors and pro- 
duce voltage drops in opposition to the input 
voltages, an effect which becomes larger at 
higher frequencies. 



Figure 29. Background of magnetic noise re- 
corded during straight and level flight of a 
G-21A airplane. 


The last three stages have large cathode 
resistors to increase their stability. In order 
not to leave the grids too strongly negative be- 
cause of the cathode resistor drops, the constant 


positive voltage across R139 is added to the 
grid bias of each of these stages. 

The cathodes of tubes V106 and V106' are 
tied together by a jumper across their cathode 
resistors. This jumper may be removed to per- 



Figure 28. Background of magnetic noise re- 
corded during straight and level flight of a 
PBY airplane. 


mit use of the cathode circuit as a low-imped- 
ance output circuit. Tube V107 is a voltage 
regulator for stabilizing the filament supply 
to the critical first two stages. 

VlOl and V102 are operated in the plate 
current cutoff region. They must have uniform 
characteristics, and it is essential for high 
amplification that the cutoff be sharp. There- 
fore the tubes used in these sockets require 
special testing and selection on a special tube 
tester designed to check these critical char- 
acteristics.^'* 

The recorder is a standard Esterline-Angus 
type AW 0. 5-0-0. 5 recording milliammeter, with 
a chart speed of IV 2 inch per minute, revised 
to include a lighting system in the case. 


3 5 THE ORIENTOR CIRCUITS 

The lower half of Figure 18 shows the 
battery circuit for electrically aligning the 
orienting magnetometers so that they will 
maintain the detector strictly parallel to the 
field, and it also gives the circuits by means of 
which the orienting magnetometers control the 
servo motors. 


CONFIDENTIAL 



36 


THE AN/ASQ-1 DETECTION EQUIPMENT 


3.5.1 Magnetometer Alignment 

Circuits 

Resistors R142, R144, R189 and the two 
halves of R191 are connected in series as a 
potentiometer across battery B102. R191 and 
R189 constitute coarse and fine adjustments for 
sending a small neutralizing current in either 
direction through the inner magnetometer 
bridge. (The orientors are labeled as inner or 
outer from the location of their respective 
gimbals.) Figure 24 is a detail of the connec- 
tions. 

Test switch SW104, with BIOS and R145, 


tion. If the neutralizing current is adjusted so 
that these test signals are equal, the element 
assembly is then at the proper position so far 
as rotation about the axis of this orientor is 
concerned. 

An identical circuit adjusts and tests the 
neutralization of the outer orientor bridge. 


3.5.2 Orienting Amplifier Circuits 

That part of Figure 18 which includes the 
amplifier circuit for the inner orientor is re- 
peated in Figure 25. The spike pattern from 



Figure 30. Schematic diagrams of the universal magnetometer head. 


increases or decreases the neutralizing current 
slightly and so provides a means of testing for 
parallelism between the detector and the ambi- 
ent field. A small change in the neutralizing 
current causes the magnetometer assembly to 
rotate to a new position. As a result of the 
change, the detector produces an output signal 
on the recorder. An exactly equal change in the 
original neutralizing current is made in the 
opposite direction, and a detector signal is 
again obtained. These two signals will be of 
equal amplitude only if the detector element 
was initially parallel to the field and was thus 
deoriented by the same amount in each direc- 


the magnetometer bridge is applied through 
T102 to the grids of V108 and V108' which are 
connected as a frequency doubler. V108 con- 
ducts on alternate spikes and is biased almost 
to cutoff on the intervening ones by the drop 
across C124 and R148, similar to the action of 
VI 02 in the detector amplifier. V108' passes 
those spikes which V108 does not. Figure 26 
shows the time variation of the V108-V108' 
plate potential. Since there is one pulse for 
every spike the output of this stage will show 
800 pulses per second. If the magnetometer 
head is properly oriented the pulses will be of 
equal height, but if there is misorientation 


CONFIDENTIAL 


THE ORIENTOR CIRCUITS 


37 


alternate pulses will be smaller and the pattern 
will contain a 400-cycle component. 

The purpose of the remainder of the circuit 
is to filter, shape, and amplify this 400-cycle 



Figure 31. DT-3/ASQ-1 universal head, with 
streamlined housing removed. 

component whenever it exists. The frequency 
doubler output is sent to the grid of VllO 
through the filter R156, C132, C134, R158. 
This tube is a tuned inverse feedback stage. 
The plate output of VllO is fed back (through 


R166, C138, C136, R162, R164, and C140) to 
the grid in proper phase to oppose the input 
signal for all frequencies except 400 cycles. 
The latter frequency is not passed by the filter. 
The result is to weaken all the signal except the 
400-cycle component. The next two stages, 
VllO' and V112, constitute a feedback amplifier 
whose purpose is to amplify the 400-cycle com- 
ponent and bring the output closer to a sinus- 
oidal shape. As indicated in Figure 26 the 



Figure 32. DT-3/ASQ-1 magnetometer head as- 
sembly. 


phase of the output and direction of rotation 
of the servo will depend on whether V108 or 
V108' passes the larger pulses. The outer orient- 
ing magnetometers are served by an identical 
system, companion to the one just described. 

Circuit Details. Cl 52 increases the output by 
being tuned to resonate at 400 cycles with T104 
and the servo winding. R180 serves to suppress 
spurious oscillations in the output stage. Just 
as in the detector circuit, V108-V108' must be 


CONFIDENTIAL 


38 


THE AN/ASQ-1 DETECTION EQUIPMENT 


a tube carefully selected for balance. C128 and 
C130 help to make the V108-V108' plate voltage 
pulse into a broader “sawtooth’' — closer to the 
desired sine wave than the narrow spike pat- 
tern. When either tube conducts, these con- 
densers partially discharge and so hold the 



Figure 33. DT-3/ASQ-1 motor assembly show- 
ing proportional control system coil. 

plate potential relatively low for some time 
after the spike has passed. The condenser 
charge (and so the plate voltage) must be 
gradually rebuilt after each spike by B-|- sup- 
ply current through R154 and R152. 

The cathode bias elements C154-R148 and 
C126-R150 are very important in determining 
the dynamic response of the orienting system. 


In the steady state V108 and V108' are so 
strongly biased that only the tops of the grid 
voltage peaks cause current flow. If a sudden 
shift of the magnetometer takes place, the 
input peaks will instantly become unbalanced. 
Due to the long time constant of the bias ele- 
ments the average biases will not reach their 
new steady values until several peaks have 
occurred. During this time the 400-cycle com- 
ponent of the output will be larger than normal, 
and greater restoring torque on the magnetom- 
eter head will result than would otherwise be 
obtained. This tends to speed up the mechanical 
response of the system. 

As the head reapproaches the normal orienta- 
tion the peaks approach balance faster than the 
average bias, resulting in reversal of phase of 
the servo motor voltage and, therefore, in the 
production of a back torque which stops the 
system at the normal position and prevents 
overshooting. Such a “rate circuit” therefore 
acts as an anti-hunt device. 

This completes the discussion of the AN/ 
ASQ-1 circuits. 


3^ PERFORMANCE CHARACTERISTICS 
OF AN/ASQ-U" 

Sensitivity of Detector 

The sensitivity of the detector system is ad- 
justable by steps over a wide range. At the 
lowest value, a sinusoidal magnetic signal at 
0.3 c must have an amplitude of 125 gammas 
to produce a full-scale deflection on the re- 
corder. At the highest sensitivity and the same 
frequency, a signal of one gamma will produce 
a full-scale deflection. The sensitivity normally 
used is intermediate and the choice in a par- 
ticular case will depend upon the magnetic 
noise produced by the aircraft and by the vari- 
ations in the earth’s fleld. The available range 
is more than adequate, because the signal re- 
ceived from a submarine will rarely exceed 
100 gammas and submarine signals smaller 
than one gamma will probably not be recog- 
nizable because of the background noise. 

Noise Levels 

The inherent background noise is shown in 


CONFIDENTIAL 


PERFORMANCE CHARACTERISTICS OF AN/ASQ-I 


39 


Figure 27. At least part of this output is caused 
by time variations of the earth’s magnetic 
field. 

Figure 28 shows the background noise re- 


and level flight of a Grumman G21-A airplane. 
The maximum amplitude in this case is also less 
than 0.25 gamma. The noise recorded during 
rapid maneuvers may be considerably larger, 



© 

(£> 



V-502 

V-503 


Figure 34. AM-9/ASQ-1A unit, schematic circuit diagram. 


corded by AN/ASQ-1 equipment during straight 
and level flight of a PBY airplane. On the chart, 
time is shown as progressing from left to right, 
with the interval between lines representing 
30 seconds. The maximum amplitude during the 
interval shown is about 0.25 gamma, so that a 
submarine signal of one or two gammas would 
be detectable. Figure 29 shows the noise re- 
corded by the same equipment during straight 


depending on the uncompensated magnetic 
fields of the particular aircraft. 

Precision of Stabilization 

The overall performance of the AN/ASQ-1 
equipment is closely related to the precision 
with which the stabilizer system keeps the de- 
tector element oriented in the earth’s magnetic 
field. The maximum stabilizer error of AN/ 


CONFIDENTIAL 


40 


THE AN/ASQ-1 DETECTION EQUIPMENT 


ASQ-1 during usual aircraft maneuvers is only 
about five minutes of arc. The magnetic noise 
recorded during aircraft maneuvers, which 
arises from magnetization and eddy currents, 
will establish a higher threshold of noise than 
can be attributed to the orientor errors. 

Adjustments in Flight 

The deviation of the magnetic state of the 
detector from perfect magnetic balance is in- 



Figure 35. AN/ASQ-IA equipment. 


dicated continuously by the balance meter on 
the panel of the control unit. Since this devia- 
tion depends on the magnitude of the earth’s 
field, readjustment will be necessary if the air- 
craft travels to a new area where the earth’s 
field has a markedly different value. However, 
if a decrease of 20 per cent in sensitivity is 
allowable, then an increase or decrease of 1,000 
gammas in the earth’s field can occur before 
readjustment is necessary. 

The need for readjustment of the stabilizer 
system neutralization circuit arises only be- 
cause of the drift of circuit constants with time. 
Under reasonable conditions of operation the 
adjustment of orientation will be required about 
twice a day.^® 


varying supply voltage, variable temperature, 
severe vibrations, and high humidity. The 
AN/ASQ-1 operates equally well with supply 
voltages from 22 to 29 volts, and the output is 
practically unaffected by sudden changes of 
supply voltage within this range. 

The equipment is designed and tested for 
operation at temperatures between — 20 and 140 
F. The only effect of large temperature varia- 
tions within this range is a small change in 
detector sensitivity. This is not a serious defect 
since the sensitivity is readily adjustable by 
means of the control previously described. Be- 
fore being assembled, circuit components are 
selected, processed, and tested for stability 
under varying temperatures. 

The most stringent requirements on design 



Figure 36. Mark IV B-2 magnetic airborne de- 
tection circuits and recorder. 


Serviceability 

Reliability of operation is a most important 
consideration in the design and manufacture 
of equipment to be used under conditions of 


and construction are imposed by the severe 
vibration under which the equipment is used. 
It is accordingly made mechanically rugged 
and provided with antishock mountings. The 


CONFIDENTIAL 



THE AN/ASQ-IA SYSTEM, WITH UNIVERSAL HEAD 


41 


electronic circuits are designed for low micro- 
phonic effects. Each unit is tested for satisfac- 
tory operation while subjected to violent vibra- 
tion on a shaking table.^^ 

Consideration has been given to the problem 
of operation under conditions of high humid- 
ity. Long-term stability and reliability have 
been achieved through the use of high-quality 
components, careful choice of insulating mate- 
rials, and thorough impregnation of parts with 
moistureproof materials. 


^ ■ THE AN/ASQ-IA SYSTEM, WITH 
UNIVERSAL HEAD 

The AN/ASQ-1 system so far considered 
used the DT-l/ASQ-1 magnetometer head as- 
sembly which permitted rotation about two 
axes. This is satisfactory in the polar and mid- 
dle latitudes, but in the equatorial regions 
where the magnetic dip angle is less than ±20° 
serious trouble results. To counteract certain 
heading changes and angles of bank of the 
plane, the gimbals are required to rotate at 
speeds much greater than the drive motors can 
provide. The gimbals may also lock in a dead- 
center position.-^ Changes in the method of 
mounting-^’ -- the two-axis head will overcome 
this trouble, but these permit a winding up 



Figure 37. Mark IV B-2 magnetometer head 
assembly. 


and eventual breaking of the electrical leads 
as the airplane executes 360° turns. 

The difficulty was solved in the DT-3/ASQ-1 
head,^^' the so-called universal head, by add- 
ing a third axis of rotation. MAD systems in- 
corporating this head are labeled AN/ASQ-IA. 
The essential mechanical parts of a universal 
head are shown in Figure 30. The detector ele- 
ment (1) is mounted rigidly through the orien- 


tor plate (2), which is pivoted in the closed 
gimbal (3). This pair of pivot bearings forms 
one axis AA', and the bearing positions of the 
closed gimbal frame form another axis BB' at 
right angles to it. These bearings on the closed 
gimbal are set in the open-fork gimbal (4). 
The center of the fork forms with suspending 
shaft (5) the third (slow-follow) axis, CC'. 
This shaft is supported by a bearing (6) which 
is fixed to the airplane so as to hold axis CC' 
parallel to the line of flight. 

By means of electronic equipment previously 
described the stabilizer elements (7, 8) on the 



Figure 38. Mark IV B-2 magnetometer head. 


orientor plate control tw^o motors (9, 10). 
Motor (10) effects stabilization about the sec- 
ond axis by means of shaft (14), pinion (12), 
and gear (13). Motor (9) does the same about 
the first axis, with shaft (14), bevel gears (15, 
16), pinion (17), and gear (18). 


CONFIDENTIAL 


42 


THE AN/ASQ-l DETECTION EQUIPMENT 


All the parts mentioned are mounted directly 
or indirectly on shaft (5) and rotate with this 
shaft about the third axis, through bearing (6) 
and a similar bearing (19) near the motor end. 
This rotation is the slow-follow motion, and 
motor (20), rigidly attached to the outer bear- 
ing structure, provides stabilization of the 
slow-follow axis. 

One simple type of difficulty of the two-axis 
mounting may be understood from this draw- 
ing. Suppose the assembly to be installed with 
axis BB' fixed parallel to the line of flight of 
the plane, as is usual with DT-l/ASQ-1. Then 
for level flight BB' would be horizontal. At the 
magnetic equator the detector should lie in the 
horizontal plane for level flight, which means 
that the orientor plate (2) should lie in the 
vertical plane. But with BB' fixed any vertical 
alignment of plate (2) places the detector point- 
ing parallel to BB'. No other azimuths in the 
horizontal plane would be accessible to the de- 
tector. The MAD system could only function 
correctly when the airplane was heading due 
north. If the system were installed with BB' 
fixed in a vertical position the detector would 
continuously rotate perpendicular to BB' as the 
aircraft executed a spiral search pattern in 
level flight, and the leads would be broken. 
Provision for rotation about the third axis CC' 
whenever necessary removes the difficulty. 

Figure 31 shows the DT-3/ASQ-1 assembly 
with its streamlined housing removed. Figure 
32 is a view of the head proper. The discussion 
of complicated cases involving various bank, 
pitch-heading angles of the plane in locations 
of varying dip angle can best be carried out 
mathematically^^ -^ or with a movable model. 
The results show that to serve its purpose the 
motion about the CC' axis must introduce a 
bank of the instrument to counteract partially 
any bank of the plane. The motion can be as 
slow as the turn of the plane and does need to 
be very precise. 

To accomplish this, rotations about CC' are 
made to accompany and be proportional to any 
rotations about AA' caused by the servos in 


response to aircraft maneuvers. Coils L407 and 
L408 in Figure 32 pick up stray field from the 
detector element. The voltage induced in them 
depends upon the angle between the detector 
element and the outer frame and so is respon- 
sive to rotations about AA'. Figure 33 shows 
coils L410 and L411 which are carried by the 
support frame and so are fixed in position with 
the aircraft. These coils are fed 400-cycle cur- 
rent from the detector element driver. Coil 
L409 is fastened to the rotating members. The 
voltage induced in it at any instant will depend 
upon its angular position with respect to L410 
and L411, and so this voltage will be responsive 
to any rotation of the head assembly about 
axis CC'. 

The voltage from L407 and L408 is now fed 
into an auxiliary amplifier (labeled AM- 
9/ASQ-lA) in series opposition to the voltage 
from L409. Now any rotation about AA' caused 
by the fast servo in response to aircraft maneu- 
ver will create a voltage unbalance in this am- 
plifier which will actuate motor (20). This 
motor will cause a slow rotation about CC' until 
the resulting voltage change in L409 counter- 
balances the original voltage change in L407- 
L408 and so removes the driving force. 

The universal head obviates the difficulties 
mentioned for all operating conditions except 
with bank angles of over 40° near the magnetic 
equator. This latter restriction is not serious. 

Figure 34 is the schematic circuit diagram 
of the AM-9/ASQ-1A amplifier. The V503 stage 
amplifies the constant 400-cycle voltage from 
the detector element driver entering at 7, J in 
order to energize the field of the servo motor. 
Stages using tubes V501, V501', and V502 am- 
plify any 400-cycle voltage fed in at 77, G from 
the coil combination (L407 + L408 — L409) 
and send it to the other windings of the motor. 

The complete AN/ASQ-IA equipment is 
shown in Figure 35. In its finished state it rep- 
resents considerable improvement in rugged- 
ness and reduction of weight over the older 
model Mark IV B-2 which is shown in Figures 
36 to 38. 


CONFIDENTIAL 


Chapter 4 

MAD SIGNAL STUDIES 


AS DEVELOPMENT WORK continued and MAD 
_l\_ equipment reached the Armed Services, the 
need grew for more exact information about 
field strength variations. It was evident that 
the use of an actual submarine and aircraft was 
not practicable.^ In addition to the difficulties 
in scheduling and carrying out such trials, the 
wide range of magnetic dip angle and state of 
submarine magnetization encountered in com- 
bat could not readily be simulated. 

The MAD signal is determined by a number 
of variable factors, including the distance from 


Table 1. Some submarine moments measured 
under various circumstances. All values are in 
units 10’^ times a cgs unit. 


Submarine 

Approxi- 

mate 

total 

moment 

Longi- 

tudinal 

com- 

ponent 

Trans- 

verse 

com- 

ponent 

Verti- 

cal 

com- 

ponent 

S-44 

23 




USS 178 

10.3 




R-16 

3 




USS 258 

10 




USS 253 

7.6 




USS 167 

5 




USS 282 

26 




British “T” Class 

14 




USS 172 

14 




German U-boat 

24 




R boat 

1 




USS 204 

5 




German U-boat 

17 




German U-boat 

5 

4 

4 

1 

German U-boat 

5 

0 

-1 

-3 

German U-boat 

10-20 

10 X 

2 X 

5 



cosine of 

sine of 




heading 

heading 




angle 

angle 



the target submarine, the path of the aircraft, 
nature of the submarine’s field, and the response 
of the electronic circuit. The characteristics of 
the submarine’s field depend upon its magnetic 
history, which determines its permanent mag- 
netic moment, and its location and direction 
at the time of contact, which determine its in- 
duced moment and the resultant field pattern. 
Table 1 lists a few of the submarine moments 
measured in various circumstances during the 
war.2> 3 


Because of the wide range of variables which 
must be investigated, the use of models seemed 
a suitable approach to the problem. It is pos- 
sible to reproduce with great exactness the 
phenomena associated with the magnetic ob- 
jects with models, if the relative physical di- 



Figure 1. A. Vertical cross section through a 
typical submarine field. The short lines at the 
positions D represent various successive positions 
at the detecting magnetometer element. They all 
make the same angle 6 with the horizontal. 

B. MAD signal received by aircraft passing di- 
rectly over submarine. 

mensions and distribution of magnetism in the 
object are carefully reproduced at the reduced 
scale. The model studies here described pro- 
vided a foundation for the design of the auto- 
matic trippers and the dual automatic AN/ 
ASQ-2 system taken up in Chapter 5. They also 
indicated directions for the improvement of 
operating tactics in the field. 

Two classes of investigation were carried 
out. In the static contour studies the anomaly 
field above various submarine models was 
mapped and statistical conclusions were drawn 


CONFIDENTIAL 


43 


44 


MAD SIGNAL STUDIES 


on various features, such as the most frequently 
occurring positions of maximum field strength. 
In the dynamic signal studies the submarine 


TABLE DETECTOR ELEMENT MAP 



Figure 2. Arrangement for plotting static con- 
tour maps. 


N 



= 5 X 10" cgs = 1 X 108 cgs 

My = 0 h = 2001 

Angle of dip = 60° 


Figure 3. Contour chart of submarine at a large 
dip angle, heading N. 

model was moved past a standard AN/ASQ-1 
detector (or vice versa) at various speeds and 
orientations which might occur in combat. The 


resulting recorder traces were studied statisti- 
cally and in detail. 


4 1 STATIC CONTOUR STUDIES 
Equipment 

The magnetometer head may be simulated in 
the model by using a detector with a fixed 
orientation determined by the prevailing mag- 
netic field in the location to be investigated. 
Reproduction of the orienting system is not 



Figure 4. Contour chart of submarine at a large 
dip angle, heading SE. 


necessary. The actual magnitude of the mag- 
netic moment associated with a submarine need 
not necessarily be reduced by the same scaling 
factor as the physical dimensions. An appro- 
priate reduction may be chosen to suit the 
circuit constants of apparatus associated with 
the model. Having chosen an arbitrary value 
of magnetization convenient for use with asso- 
ciated equipment, one must then calculate a 
scaling factor which indicates the relationship 


CONFIDENTIAL 



STATIC CONTOUR STUDIES 


45 


between the magnetic moment of the actual 
object and that of the scale model. This calcu- 
lation can be simplified in the case of a sub- 
marine by considering the magnetic moment 
to be that of a concentrated dipole. It has been 
shown that, at distances comparable to or 
greater than the length of a submarine, the 



Figure 5. Contour chart of submarine at a large 
dip angle, heading W. 


field due to the distributed magnetism of the 
submarine differs from that due to a dipole of 
like total moment by small amounts, the dif- 
ference being of the order of 7 per cent when 
the separation is the same as the length of the 
submarine and decreasing as the separation is 
increased. Thus, if a greater separation is 
chosen, quite accurate calculations may be made 
using dipole equations. Figure lA shows a ver- 
tical section through a typical submarine dipole 
field. 

If the system comprising submarine and de- 
tector is reduced to a size convenient for repro- 
duction in a laboratory, several problems at once 
present themselves. In the first place, the change 
in field to be measured is of the same order as 
the differences in field intensity which abound 
in the average electrical laboratory. In addition. 


investigation is limited to the single magnetic 
latitude at which the laboratory is located. The 
problems can be overcome if the earth's field 
can be neglected and only the field due to the 
submarine model measured. The effect of the 
earth’s field may be eliminated by simulating 
the field of the submarine in the model by 
means of an alternating field of a given fre- 
quency, with magnitude and direction adjust- 
able at will, and making the detector sensitive 
only to alternating fields of that frequency. 
Since such a detector is sensitive only to the 
single frequency alternating field, it is unaf- 



Figure 6. Contour chart of submarine at low 
dip angle, heading E. (Dashed contours repre- 
sent negative y values.) 


fected by the earth’s steady magnetic field and 
the magnetic gradients of the laboratory. In- 
vestigations can be carried out for any mag- 
netic latitude since only the magnetization of 
the submarine and the relative orientation of 
the detector element and the field of the sub- 
marine need be varied in order to simulate 
operation at various latitudes. 


CONFIDENTIAL 


46 


MAD SIGNAL STUDIES 


The total moment associated with the sub- 
marine may be conveniently represented by 
means of three component moments which add 
vectorially to give a resultant of the proper 
magnitude and in the proper direction. The 
components may be chosen in such manner 
that one of them lies along the fore and aft or 
longitudinal axis of the submarine, a second 



Figure 7. Contour chart of submarine at low 
dip angle and 30° heading. 


along the vertical axis of the submarine, and a 
third along the athwartship or transverse axis 
of the submarine. These components may be 
designated as the longitudinal, vertical, and 
transverse moments, their positive directions 
being taken as toward the bow, down, and to- 
ward port, respectively. The three component 
moments may be generated in three mutually 
perpendicular coils so oriented in space that 


the moments lie along the chosen axes of the 
submarine. If these coils are excited with direct 
current or properly phased alternating current, 
a field, the direction and magnitude of which 
will be determined by the magnitude of the 
excitation of the three coils, will be generated. 
It can be shown that in the case of alternating 
current excitation the polarity or direction of 



Figure 8. Contour chart of submarine at low 
dip angle, heading N or S. 


the component moments of the submarine may 
be reproduced in the model by appropriately 
shifting the relative phases of the excitations. 
Direction or polarity may then be determined 
through the use of a reference signal, with re- 
spect to which the relative phases of the exci- 
tation signals may be measured. If such excita- 
tion is used, the output of the pickup coil will 
be an alternating voltage, the rms magnitude 


CONFIDENTIAL 



STATIC CONTOUR STUDIES 


47 


of which may be measured by a vacuum tube 
voltmeter. 

A magnetic plotting table utilizing the prin- 
ciples above discussed was constructed,^ using 
throughout a scale of 1 centimeter to 10 feet. 
As shown schematically in Figure 2, the ap- 
paratus comprises a drafting table, beneath 
which is mounted the model submarine and to 
the surface of which a suitable charting paper 


table top is taken to represent a chosen altitude 
surface and adjustments in the height of the 
elevator simulate changes not only in the alti- 
tude of the airplane bearing the detection 
equipment but also in the submersion of the 
submarine. The 500-cycle excitation for the 
three coils is provided by means of a single 
oscillator, a separate amplifier being provided 
for each of the three coils. The pickup coil is 



Figure 9. Variation of intensity and position of “peak” of submarine field with elevation. 


may be secured. The detecting element is ar- 
ranged to be moved over the chart and means 
are provided for marking its position thereon 
at any time. 

The submarine model comprises three mu- 
tually perpendicular coils mounted on a turn- 
table capable of 360° rotation. This turntable 
is mounted on a screw-type elevator, by means 
of which its separation from the top of the 
drafting table may be adjusted. The drafting 


arranged to rotate about a horizontal axis, the 
orientation of which is fixed in respect to the 
table top, this axis being the perpendicular 
bisector of the longitudinal axis of the coil. One 
direction on the table top, along which lies the 
projection of the longitudinal axis of the pickup 
coil, is chosen as (magnetic) north and all head- 
ings of the submarine are measured with this 
as a reference. The horizontal axis about which 
the coil may be rotated then extends in the 


CONFIDENTIAL 


48 


MAD SIGNAL STUDIES 


east-west direction so that the angular position 
of the detector coil corresponds to the dip angle. 
The voltage induced in the coil as it passes over 
the field of the submarine is measured by means 




Figure 10. Field variations and response signals 
for a case of dual MAD installation at the wing 
tips of an airplane. 


of a vacuum tube voltmeter. This meter is cali- 
brated to read directly in gammas in the fol- 
lowing manner. 

The detector coil is placed directly over the 
center of the submarine and is oriented verti- 
cally. Excitation is then supplied to the coil 
generating the vertical moment of the sub- 
marine, and the separation between the center 
of the submarine and the coil is measured. The 
amount of the excitation is varied, using the 
gain control of the appropriate amplifier until 
the output vacuum tube voltmeter reads a con- 
venient value, say, 10. The scale on which read- 
ing is obtained is noted and the reading is des- 
ignated as that corresponding to a 10-gamma 
signal. The excitation supplied to the submarine 
coils is read in amperes. Using the separation 
between detector and submarine previously 
noted and the arbitrarily chosen value of the 
field at the detector, the moment produced by 
the coil is calculated using dipole equations. 
The calibration factor relating moment in cgs 
units and excitation current in amperes may 
then be calculated for the coil generating the 
vertical moment. 


The calibration factors for the other two 
submarine coils may then be determined with 
reference to that just determined. For this pur- 
pose the detector is reoriented in such manner 
that it is parallel to the longitudinal axis of the 
submarine. Excitation is then supplied only to 
the submarine coil generating the longitudinal 
moment, the separation between the detector 



Figure 11. Sum and difference contour chart for 
50-foot separation of detectors, with plane head- 
ing N at all points. 


and the coil being held at the value used in the 
first calibration. The excitation is then varied 
until the detector voltmeter reads one-half the 
value previously used. (When the axes of the 
detector coil and the coil in which the field is 


CONFIDENTIAL 


STATIC CONTOUR STUDIES 


49 


generated are parallel, the output of the coil is 
one-half the output which results when the axis 
of the detector coil forms an extension of that 
of the generating coil.) The excitation current 


MysSXlO^CgS 

Ml = 0 

Mj-O N 

h=200’ ,r 

ANGLE OF DIP * 70* 

S*0* 

PLANE HEADING * 90* 

CRAB ANGLE =0* 

SUM 

DIFFERENCE 




Figure 12. Sum and difference contour chart for 
50-foot separation of detectors, with plane head- 
ing E at all points. 


in amperes is then read and the calibration 
factor for the longitudinal moment calculated 
from that for the vertical moment, using sim- 
ple proportions. The calibration factor for the 
transverse moment is obtained by a similar pro- 
cedure, the detector coil being oriented with its 
axis parallel to the transverse axis of the sub- 
marine. 

In addition to determining the calibration 
factors for the coils generating the three mo- 
ments, it is also necessary to determine the 
phasing of the excitation in each for the pur- 


pose of simulating the polarity or direction of 
the moment generated thereby. For this purpose 
the phase of the excitation in each coil must be 
measured relative to that of a reference signal 
and some phase relation designated as repre- 
senting one polarity of moment. For this meas- 
urement the detecting element is first placed in 
its vertical orientation directly over the center 
of the submarine model. The lower end of the 
element is marked and thereafter designated as 
the N pole. Excitation is then supplied to the 
coil generating the vertical moment for the 



Figure 13. Sum and difference contour chart for 
submarine at low dip angle. Detector separation 
is 50 feet. 


submarine. The excitation to the submarine coil 
is also impressed upon the horizontal sweep 
circuit of a cathode-ray oscilloscope while the 
signal from the detector is impressed upon the 
vertical axis input of the same oscilloscope. 


CONFIDENTIAL 


50 


MAD SIGNAL STUDIES 



ABC 


Figure 14. Model signals. Target is vertical 
dipole; dip angle 70°; blimp heading N at 20 
knots and 200 feet elevation. Lateral displace- 
ment of path from target center: (A) 0 feet; 
(B) 100 feet; (C) 200 feet. 



ABC 


Figure 15. Model signals. Target is vertical 
dipole; dip angle 70°; blimp heading N at 80 
knots and 200 feet elevation. Lateral displace- 
ment of path from target center: (A) 0 feet; 
(B) 100 feet; (C) 200 feet. 



Figure 16. Model signals. Target is vertical 
dipole; dip angle 70°; blimp heading N at 20 
knots and 400 feet elevation. Lateral displacement 
of path from target center: (A) 0 feet; (B) 100 
feet; (C) 200 feet. 



ABC 


Figure 17. Horizontal dipole directed N, dip 
angle 70°, blimp heading E at 40 knots, 200 feet 
elevation. (A) 0 feet displacement; (B) 100 feet 
displacement; (C) 200 feet displacement. 




ABC 

Figure 18. Horizontal dipole directed N, dip 
angle 30°, blimp heading N at 20 knots, eleva- 
tion 400 feet. (A) 0 feet displacement; (B) 100 
feet displacement; (C) 200 feet displacement. 




ABC 

Figure 19. Horizontal dipole directed E, dip 
angle 30°, blimp heading E at 20 knots, 200 feet 
elevation. (A) 0 feet displacement; (B) 100 
feet displacement; (C) 200 feet displacement. 


CONFIDENTIAL 


STATIC CONTOUR STUDIES 


51 


The two signals will ordinarily be either in 
phase or 180 ° out of phase, depending upon the 
position of the reversing switch associated with 
the vertical moment coil. Since the positive 
vertical moment of a submarine is always taken 
as downward, the signal picked up by the detec- 





loscope, as described above. Since the longitu- 
dinal moment of the submarine is taken as 
positive when it extends from stern to bow 
thereof, the geometry of the system indicates 
that a negative signal will be received by the 
detector. Therefore, if the trace on the oscillo- 





Figure 20. Horizontal dipole directed E, dip 
angle 70°, blimp heading E at 40 knots, 200 feet 
elevation. (A) 0 feet displacement; (B) 100 
feet displacement; (C) 200 feet displacement. 


Figure 21. Vertical dipole directed N, dip angle 
30°, blimp heading N at 20 knots, elevation 400 
feet. (A) 0 feet displacement; (B) 100 feet dis- 
placement; (C) 200 feet displacement. 


tor may be designated as positive. The sign of 
the slope of the trace on the oscilloscope is noted 
and the position of the reversing switch desig- 
nated as positive. 

The submarine model is then placed on a 
north heading, one end of the model always 
being designated as the bow, and the detector 


INPUT SI 
FROM 3 
DETECTOR 5| 



Figure 22. Demodulator for a-c dynamic signal 
system. 


is oriented with its axis parallel to the longi- 
tudinal axis of the submarine and with its N 
pole to the north. The coil generating the longi- 
tudinal moment of the submarine is then ex- 
cited and the relative phase of this excitation 
and the signal picked up by the detector com- 
pared through the use of the cathode-ray oscil- 


scope has a slope opposite in sign to that ob- 
served with the vertical moment, the position of 
the reversing switch is marked as positive; 
otherwise, it is marked negative. 

The same procedure is repeated for the coil 
generating the transverse moment, the positive 
transverse moment of the submarine being 
taken as extending from east to west while the 
submarine is on a north heading. In this case 
the detector is oriented with its N pole to the 
west so that a negative signal is again to be 
expected. If the slope of the trace on the oscillo- 
scope is opposite in sign to that observed using 
the coil generating the vertical moment, the 
position of the reversing switch is marked posi- 
tive as in the case of the coil generating the 
horizontal moment. 

A further determination of polarity is made, 
using the detector in its vertical orientation and 
exciting all three coils, the phases of the three 
excitations having previously been adjusted to 
be the same. The relative phases of the excita- 
tion to the coils and that of the signal picked 
up by the detector are compared, using the 
cathode-ray oscilloscope. The total resultant 
moment of the submarine is taken always to 


CONFIDENTIAL 



52 


MAD SIGNAL STUDIES 


point downward when positive so that, if the 
trace has a slope of the same sign as that ob- 
served in the case when only the vertical mo- 
ment coil is excited, the signal may be said to 
be positive. This fact is noted for future use 
in determining the sign of signals. It should be 
noted that if an overflashed submarine is to be 
reproduced, the vertical moment must be given 
a negative polarity. 


of H in the vertical section through the sub- 
marine, these charts show lines of constant 
magnitude of the component of H parallel to 
the earth's field throughout a horizontal plane 
above the submarine. The charts can be most 
easily described by specifying the location of 
the “peaks” or point of maximum anomaly 
field strength."* Table 2 is a compilation of the 
most usual cases for north magnetic latitudes. 


-REPETITION OF A 
ONE SECOND 


TRACE 


EARLIEST MAXIMUM VALUE 
OF GRAPHIC 0UTPUT = + 0.2y 


EARLIEST MAXIMUM VALUE OF 
ELECTRICAL OUTPUT =t0.4y 
OCCURS 2.04 SECONDS BEFORE 
NEAREST APPROACH TO 
SUBMARINE 


INTERMEDIATE MAXIMUM VALUE 
OF GRAPHIC OUTPUT=-8.2 


INTERMEDIATE MAXIMUM 
= -8.0y OCCURS 
0.05 SEC AFTER 
NEAREST APPROACH 


LATEST MAXIMUM 
/VALUE OF GRAPHIC 
0UTPUT=+3.7y 

I I 

LATEST MAXIMUM 
+ 4.4 yOCCURS 
2.12 SEC AFTER 
NEAREST APPROACH 



AIRPLANE HAS 500 FEET TO GO 
TO POINT OF NEAREST APPROACH 


AIRPLANE 500 FEET 
BEYOND POINT OF 
NEAREST APPROACH 


Figure 23. Specimen record obtained by the a-c dynamic signal technique. 


Contour Charts 


Sixty contour charts were made up""’ covering 
various combinations of the variables over the 
following ranges. 


Elevation : 

Transverse 
moment : 

Vertical moment: 

Longitudinal 
moment : 

Submarine 
heading : 

Dip angle : 


200 - 400 feet 

0 - 0.18 X 10^ cgs units 
0 - 5 X 10® cgs units 

0 - 5 X 10^ cgs units 

0- 315° 

0- 90° 


Typical cases are shown in Figures 3 to 8. 
Whereas Figure lA shows the lines of direction 


The patterns for south magnetic latitudes 
are symmetrical to those here listed. Patterns 
for different elevations are similar, those at 
greater heights being merely weaker and more 
spread out, as indicated by Figure 9. 

Sum and Difference Contour Charts 

As will be discussed in Chapter 5, the effort 
was made in the AN/ASQ-2 dual system to get 
more precise information about the submarine’s 
location by using two laterally displaced MAD 
systems, one at each wing tip of an airplane, for 
example. Figure 10 shows the resulting signals 
for a simple case. The recorder might be made 

^ These are not identical with the peaks of the MAD 
signal, which may come at different points depending 
on the plane’s path across the contours. 


CONFIDENTIAL 


DYNAMIC SIGNAL STUDIES 


53 


to indicate the difference or the sum, or some 
other combination of the two output voltages 
which might give a better measure of the posi- 
tion of the submarine. In order to explore the 
possibilities of such a system a number of con- 
tour charts were made on the plotting table here 
described using two appropriately spaced de- 
tector coils, with their outputs added or sub- 
tracted electrically. Figure 11 illustrates a 
typical simple case. The difference voltage has 


strongly dependent on the plane’s heading, as 
is brought out by a comparison of Figure 11 
and Figure 12. One of the somewhat less simple 
cases is given in Figure 13. 


4 2 DYNAMIC SIGNAL STUDIES 

Much of the usefulness of the contour charts 
comes from the fact that the variations which 


Table 2. Summary of types of submarine field patterns to be expected in north magnetic latitudes. 



Submarine 
headings 
in degrees 


Peaks 

Dip angle 
in degrees 

Type of longitudinal 
magnetization 

Number 

observed 

Position 

(approx.) 

80 to 45 

0 or 180 

Perm, and induced 

Two 

(1+ and 1-) 

On a N-S line over submarine. 



Induced only 

Two 

(1 + and 1 — ) 

On a N-S line over submarine. 


i 45, 135, 225, 

' or 315 

Perm, and induced 

Two 

(1 + and 1 — ) 

On a line parallel to submarine. 



Induced only 

Two 

(1+ and 1-) 

On a line approx, parallel to submarine. 


! 90 or 270 

Perm, and induced 

Two 

(1 + and 1 — ) 

On an E-W line a little south of submarine. 



Induced only 

Two 

(1 + and 1 — ) 

On a N-S line over submarine. 

45 toO 

310 to 50 or 
130 to 230 

Perm, and induced 

Three 

(2+ and 1-) 
or 

(l+and2-) 

Like peaks on a line over some part of submarine. 



Induced only 

Three 

(2+ and 1-) 

On a line approx, parallel to submarine. 


50 to 130 or 
230 to 310 
(approx.) 

Perm, and induced 

Four 

(2+ and 2-) 

Lines through like peaks cross near submarine 
center. 



Induced only 

Three 

(2+ and 1 — ) 

On a N-S line over submarine center. 


opposite sense on the two sides of the sum peak, 
of course, and so it might well be used to oper- 
ate a right-left indicator. (It should be noted, 
however, that the difference will indicate the 
direction of the nearest strong peak, which is 
not always necessarily the direction toward the 
submarine.) Of course the difference voltage is 


an MAD detector would encounter on any 
chosen path through the submarine’s field could 
be determined by drawing the path on the chart 
and plotting field amplitude as a function of 
detector position. It must be noted, however, 
that the curves thus obtained will not exactly 
correspond to the output signal from the MAD 


CONFIDENTIAL 


54 


MAD SIGNAL STUDIES 


/ y / 


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t 


^ y 

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y ^ 


MAGNETIC 

NORTH 








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TYPE I 
<f> : 45® 

<r = 135® 
a = +50® 

2 = 200 FEET 

V = 180 KNOTS 






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nnn 

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500 FEET RIGHT 

horizontal: < second between heavy LINES 


Figure 24. Dynamic signals obtained by the a-c coil method. 


CONFIDENTIAL 




LEFT TRACKS RIGHT 


DYNAMIC SIGNAL STUDIES 


55 


- 

- OJ- 


MA6NETIC 

NORTH 


i 



TYPE Iff 

4> = 90» 

<r = 180® 

CC = +10® 

2 = 200 FEET 

V = 180 KNOTS 




100 FEET RIGHT 










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AA 

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n 



ruu 

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500 FEET RIGHT 

horizontal:! second 8ETWEEN HEAVY LINES 


Figure 25. Dynamic signals obtained by the a-c coil method. 


CONFIDENTIAL 


56 


MAD SIGNAL STUDIES 


equipment, because all detection systems in- 
clude reactive impedance with a definite time 
constant. The resultant filter action is such that 
variations in electric output differ appreciably 
from variations in the magnetic field, as was 
shown in Figure 23 of Chapter 3. A more ac- 
curate picture of the kind of signal to be ex- 
pected on the recorder from any given situation 



TYPE I 

^ :45« 
<f =135° 
oc =50® 




LOCATION OF PEAKS OF TRIPPER INPUT VOLTAGE 


Figure 26. Peak-to-peak amplitude graph and 
peak position map obtained from data of Figure 
24. 


may be obtained by moving a submarine model 
in the proper fashion past a detector which 
feeds an actual AN/ASQ-1 amplifier.’' 


permanent magnet, the field of which simulated 
that of a submarine, along a given path past a 
fixed detector. The detector was a standard 
MAD head with the orientors disengaged. The 
fluctuations in the ambient field in the labora- 
tory do not cause quite as much trouble here 
as in the static experiments because the 
AN/ASQ-1 filter networks discriminate against 
frequencies other than those contained in the 
usual submarine signal. The head was oriented 
at the dip angle to be simulated, and the earth’s 
field was compensated by using the bias circuit 
of the MAD detector. The orientation of the 
permanent magnet was then adjusted to re- 
produce the total field of a submarine at the 
geographical location under investigation. Pro- 
vision was made for varying both the vertical 
distance and the lateral displacement between 
the submarine model’s plane of travel and the 
detector, while the speed of the model along its 
path represented the speed of the aircraft. 
Several hundred cases were investigated.'^ The 
most usual signals were of the type shown in 
Figures 14 and 15, which simulate the records 
obtainable on a blimp traveling at 20 and 80 
knots respectively. On each of these records a 
short vertical line or a cross marks the time of 
closest approach to the target. The time scale is 
30 seconds per chart division. The sensitivity 
is not the same for the different figures, but 
it is the same for the three records of each 
figure. 

Although Figures 14 and 15 show the most 
usual case, there occur conditions where the 
peaks for 0, 100, and 200 feet lateral displace- 
ment of the path from the target have other 
relative magnitudes (Figures 16 to 20), or 
where corresponding peaks are not of the same 
sign at each displacement (Figure 21). Such 
complications are to be expected, of course, in 
view of the varied types of static contour maps 
which may occur. 


The Permanent Magnet System 

Two systems were used for simulating dy- 
namic signals. In the first a trolley moved a 

^ Of course any of the possible signal patterns may 
be derived mathematically if suitable expressions are 
known, or can be assumed, for the behavior of the 
amplifying circuits. For work in this line see refer- 
ence 6. 


The A-C Coil System 

The use of the model equipment with which 
the contour charts were made for the study of 
dynamic signals is entirely possible, if means 
are provided for moving the detecting element 
across the surface of the charting table at a 
scaled speed and for introducing the signal 


CONFIDENTIAL 


DYNAMIC SIGNAL STUDIES 


57 


picked up thereby into a replica of standard 
MAD equipment. In view of the fact that field 
patterns for a submarine of given magnetiza- 
tion are similar regardless of the altitude at 
which they are measured, it will be understood 
that the speed at which the detecting element 
is moved across the charting table must be 
scaled using the same scaling factor as is used 


for this purpose. Once such runs have been 
made, the rheostat controlling the speed of the 
motor may be calibrated directly in scale miles 
per hour. 

Since the submarine model is provided with 
alternating current excitation, the output of the 
detector, as it is moved thereover, will be essen- 
tially a modulated 500-cycle wave, the carrier 


MEAN V 

■_ 

ALUE = 582 

■ 

T 

1 




ON -COURSI 
Z = 200 FE 
V= 1 20 K^ 

E 

ET 

JOTS 

■ ■ 

MEAN V/ 

,LUE = 6I5 F 

T 

■ 

1. 

1 

ifc ■ 

U 

CROS: 
Z = 2( 

4. 

5-COURSE 

DO FEET 
:0 KNOTS 

■ 

1 









1 

ALUE =365 1 

■ ■ ■ 

FT 

JL-H— 




1 . 

ON -COUR 

Z= 300 FE 
V= 120 KN 

SE 

ET 

lOTS 

1 









1 MEAN V 

1 L 

ALUE = 217 1 

-T 

liJL 

_nJj 

L 



CROSS-COURSE 

Z = 300 FEET 

V = 1 20 KNOTS 


0 100 200 300 400 500 600 700 800 900 

Figure 27. Frequency distribution of search widths in feet for peak-to-peak recorder signals greater than 
5 gammas. 


in scaling the separation between the detector 
and the submarine. 

In the model the detector is arranged to be 
moved across the plotting table on any heading 
by a towing device. Mechanism for carrying the 
detector over the submarine model comprises a 
pair of parallel tracks supported by a frame 
which may be placed on the table top and a 
wheeled carriage which bears the single detec- 
tor airplane model and may be drawn along 
these tracks by means of an electric motor. The 
relationship between motor voltage and scale 
speed may be determined through the use of a 
stop watch, several timing runs being required 


frequency being the frequency of excitation 
supplied to the submarine coils. Since the car- 
rier signal is sinusoidal, the demodulator stage 
of standard MAD equipment cannot be used in 
the model setup. It can be shown, however, that 
if a suitable demodulator circuit is substituted 
for the demodulator stage of the MAD equip- 
ment and the output of this circuit is fed 
through the remainder of the MAD detector 
equipment, dynamic signals will be recorded on 
the Esterline-Angus meter. These signals will 
in every way correspond with those actually 
obtained in practice, using the standard de- 
tector. 


CONFIDENTIAL 


58 


MAD SIGNAL STUDIES 


The model equipment includes the simple 
demodulator illustrated in Figure 22. The signal 
is introduced through an input transformer to 
the grid of an amplifier tube. The output of this 
tube is transformer-coupled to a push-pull de- 
modulator stage, and as shown in the diagram 
a reference signal from the oscillator providing 
excitation to the submarine model is introduced 



Figure 28. Possible positions of submarine cen- 
ter when MAD registers a peak at position of 
small solid circle, with plane and submarine 
courses known to be parallel. 

at the center tap in the secondary of the cou- 
pling transformer. This arrangement is neces- 
sary in order to get true reproduction of the 
signal as it goes first positive and then negative 
or vice versa, the signal from the amplifier stage 
being added to and subtracted from the refer- 
ence signal in the two sides of the demodulator 
circuit. In view of this fact it is necessary that 
the phase of the input signal correspond to that 
of the reference signal, and for this purpose 
the resistance-capacitance network indicated in 
the diagram is interposed between the input 
transformer and the amplifier tube. The output 
signal is taken from the two potentiometers 
shown in the diagram, and, since the common 


point of these two resistors is grounded, the 
signal may be used push-pull and may have 
both positive and negative polarity. This signal 
is introduced to the grids of the amplifier stage 
of the standard MAD detector unit and the out- 
put thereof is recorded on an Esterline-Angus 
meter in the same manner as in service. 

Provision was also made to record the static 
field at each point and the electric output of the 
AN/ASQ-1 circuit as well as the recorder out- 
put. Figure 23 is a specimen trace showing the 
type of information to be found on such rec- 
ords. Several thousand such test runs® were 
made with different combinations of the varia- 
bles of position and with four different com- 
binations of submarine moments. Figures 24 
and 25 are cases occurring at 50° and 10° dip 
angle, respectively. 

The chart for each test was analyzed^ and 
the peak-to-peak amplitude of the graphic out- 
put was measured for each run. This informa- 
tion was plotted against lateral separation to 
form a graph as shown in the upper part of 
Figure 26. 

In addition, peak position maps^® were made 
for the electric output. For all test runs the 
distances of the output maxima along the line 
of flight, from a vertical perpendicular through 
the center of the submarine were plotted and 
the points connected. A solid line, as shown in 
the lower drawing of Figure 26, indicates peak 
amplitudes greater than 5 gammas ; and broken 
lines, less than 5 gammas but greater than 2. 
Figure 27 is a statistical analysis of some of 
the results. 

The following conclusions were drawn from 
this series of studies. 

1. Peaks over 2 gammas high will occur in a 
range from about 250 feet before to 125 feet 
after the center of the submarine for on-course 
runs and in a range from 150 feet before to 125 
feet after the center for cross-course runs. 
These figures are based on dead-over airplane 
flights between 200 and 300 feet above all four 
submarine types studied. 

2. The search width" for the submarines rep- 

Search width is defined as that distance at right 
angles to the direction of flight at a given altitude 
within which an Esterline-Angus (E-trace, Figure 23) 
peak-to-peak amplitude of at least 5 gammas will be 
recorded. 


CONFIDENTIAL 


DYNAMIC SIGNAL STUDIES 


59 


AIRPLANE 

direction 






\\ ^ 
r\ ^ 

" vV 




\ ^ 


f 

h / 


/ 




\^- 




/ 'V , 

y\/\ 

^/^/\\ 


\ 


l' 


VERTICAL SEPARATION 200 FT 
DIP ANGLE 70“ 



SCALE 


0 ‘- :»IOOFT 

vertical SEPARATION 200FT 
DIP ANGLE 10“ 


Figure 29. Same as Figure 28, except that sub- 
marine heading may be random. 



Figure 31. Section of a typical MAD signal on a 
wrecked steamer. 


Figure 30. Same as Figure 29 — at dip angle 10°. 

sented in this study is about 600 feet at a 200- 
foot vertical separation and about 320 feet at a 
300-foot separation. 

3. The signal intensity diminishes more rap- 
idly than the inverse ratio of the vertical sep- 
arations cubed. Its magnitude decreases roughly 
as the 3.7 power of the inverse ratio of the 
two separations for on-course runs and at a 
slightly higher rate for cross-course runs. 

4. The mean value of the time index** of the 
C-trace at 120 knots for on-course runs at a 
300-foot separation is 1.75 ± 0.15 seconds. The 
frequency of the C-trace will vary directly with 
the speed and inversely with the separation 
over a limited range. 

The time index of the E-trace for speeds be- 
tween 120 and 180 knots at separations of 200 
to 300 feet lies, for the most part, between 1.0 
and 2.4 seconds. (These values are of impor- 

d The time index of an indication is the time taken to 
record its peak of minimum duration. The duration of 
a peak is shown on the record as the distance on paper 
between the start and end of the peak. 


CONFIDENTIAL 


60 


MAD SIGNAL STUDIES 


tance in fixing the frequency characteristics of 
the inputs to the d-c amplifiers in the detector 
and bomb-firing circuits.) 

Another type of generalization^^ which can 
be drawn from these records is illustrated by 
Figure 28. This shows the positions of the cen- 
ters of a wide magnetic assortment of sub- 
marines with respect to the first peak in the 
field encountered on a run made on-course with 
the target, as might occur in combat when the 
submarine heading has been observed just be- 
fore submergence or has been plotted from a 



Figure 32. Submarine signals. Altitude 100 feet, 
airplane ground speed 140 knots, submarine 50 
to 100 feet below surface. The heading of the air- 
plane was different for each pass. 

series of earlier signals. The large solid circle 
represents the first peak encountered. The ar- 
rows represent the centers of possible targets. 
The complete target outline is shown for only 
two cases to avoid the confusion which would 
result from overlapping in the diagram. Figure 
29 is a similar compilation for a situation where 
the submarine heading is not known, so all pos- 
sible headings are included. A case in the low 


magnetic latitudes is given in Figure 30. It will 
be observed that although the airplane is usu- 
ally quite close to the target when it encounters 
the first peak, there are times (Figure 30) 
when it would be better to release a bomb a few 
seconds after passing the first peak. 


4.3 TYPICAL FIELD RECORDS 

Based upon operating experience and upon 
laboratory studies with models a number of 
rules were derived for distinguishing between 
valid signals and unwanted fluctuations due to 
geological anomalies, violent fluctuations in 
power supply, etc. These rules give an indica- 
tion of the behavior of the system in the field. 

Rule 1. The first peak of a true MAD signal will not 
break sharply from the center line but will begin 
gradually. 

Rule 2. The time index of a submarine signal will 
not be less than % second nor more than 5 seconds for 
distances from the PBY plane to the submarine between 
100 and 500 feet. 

Rule 3. An MAD signal will never have more than 
five peaks and rarely more than four. 

Rule U- If the size of one peak of an MAD signal is 
off scale, then the signal will have at least one addi- 
tional peak showing above the noise level and will fre- 
quently have at least two additional peaks. 

Rule 5. Under conditions of normal noise level the 
trace of an MAD signal should be free from irregulari- 
ties, with the possible exception of the first or last peak, 
if they are small. 

Some field records^-’ illustrating these rules 
are shown in Figures 31 to 36. 


44 mad tactics 

Using the signal studies described in this 
chapter, as well as reports from the field, a 
considerable amount of research on MAD tac- 
ticsi^-iG was carried out. Probabilities of success 
were computed for various trapping maneuvers, 
tracking maneuvers, and bomb runs. Figure 37 
shows one of the more favorable and widely 
used systems: the clover-leaf pattern. Circular 
and spiral search patterns are also useful. 

Since the range of MAD is measured in hun- 
dreds of feet rather than in miles, its principal 
tactical use is in detecting, tracking, and locat- 
ing a submarine which has been sighted or 


CONFIDENTIAL 


MAD TACTICS 


61 


detected by radar at a distance and has then 
submerged as the airplane approached it. The 
general procedure in such a search and attack 
operation is as follows. 

1. A visual or radar contact is made with the 
target at a distance. 

2. The plane flies to the spot where the 
target was last observed, the target meanwhile 
having submerged. 

3. The probable point of submergence is 


5. After establishing this track, the plane 
makes a bombing attack with one of several 
types of ordnance. In some cases, the ordnance 
is released by automatic control, using the MAD 
signal. 

The nature of the attack, of course, depends 
upon the type of ordnance used. There are three 
distinct types which are known as follows : 

1. Depth charges. 

2. Mousetrap ammunition : contact bombs. 



marked and the plane executes search or trap- 
ping tactics until an MAD signal is obtained 
indicating the presence of the submarine within 
the detection range. This point is marked with 
float lights or slicks or some other marking 
device. 

4. The plane then executes tracking tactics, 
marking each successive MAD signal. The line 
of markers then indicates the submarine’s 
track. 


3. Retro-fired, rocket-propelled mousetrap 
ammunition: contact bombs. 

Depth charges and ordinary mousetrap 
bombs fall forward because of their initial for- 
ward velocity. Hence, they are released on a 
bombing run toward the target at a point suffi- 
ciently in advance of the estimated target posi- 
tion to enable them to fall on the target. 

In order to estimate the target position, the 
submarine is tracked by its magnetic anomaly ; 


CONFIDENTIAL 




62 


MAD SIGNAL STUDIES 



Figure 34. Spurious indication of geological 
origin. 



MANEUVER 



Figure 36. Comparison of signals resulting from 
maneuver of airplane and from a large buoy. 


every time the plane flies through this anomaly 
a marker is dropped. When a series of these 
markers has been put down, the pilot or bom- 
bardier is in a position to see the submarine’s 
track and to project it forward of the last 
marker. Also, from the spacing of the last two 
markers and a knowledge of the interval be- 
tween the instants at which they are dropped, 
he may predict the position of the target along 
the extrapolated track. The bombing run is then 
set up to cross this point and the bombs are 
released in a line or pattern at points along the 
airplane’s track which will center the pattern 
on the estimated target position. Thus, when 
forward falling bombs are employed, the MAD 
may be used to establish the submarine’s track, 
but because on the bombing run the bombs must 
be released before the plane arrives over the 
target, it is not used directly to establish the 


CONFIDENTIAL 


MAD TACTICS 


63 


bombing point other than by estimation, as 
mentioned above. 

Retro-bombs are used for vertical bombing. 
Hence there is no need to release them before 
the plane arrives over the target. This makes 
it possible to use the magnetic signal obtained 



when the plane flies through the submarine’s 
field to establish the bombing point. In this way 
automatic bombing controlled by the magnetic 
signal becomes possible. Thus the use of retro- 
bombs eliminates the need of predicting the 
target position by visual judgment and calcu- 
lation and substitutes a direct positive indica- 
tion which tells when the bombing point has 
been arrived at and which may be used to con- 
trol automatic bomb release mechanisms. 

In the tracking operation markers are re- 
quired. There are available for this purpose the 
following types. 

1. Slicks (aluminum, bronze, fluorescein, 
rhodomine) . 

2. Float lights (Mark IV, 3 to 5 minutes 
burning time) (Mark V, 10 to 15 minutes burn- 
ing time) . 


3. Float lights, retro-fired (Mark V). 

4. Retro-fired slicjcs which are under develop- 
ment. 

Slicks are used only in daylight operations. 
Float lights may be used at any time. Retro- 
fired float lights have a vertical trajectory and, 
therefore, mark the spot where the MAD signal 
maximum was obtained more accurately than 
do the markers which are simply dropped from 
the airplane. For example, when a float light is 
dropped from a plane moving at 200 feet per 
second ground speed at an altitude of 100 feet, 
the marker lands on the water at a point nearly 
500 feet forward of the point directly under 
the place where it was released. 

Automatic equipment for releasing both 



Figure 38. Chart of MAD action against a sub- 
marine in the Straits of Gibraltar. 


markers and bombs at the instant the maximum 
of the MAD signal is obtained, or at a pre- 
determined time thereafter, will be discussed 
in the next chapter. This automatic equipment 
may be used for marker release (especially 
retro-fired float lights) in the search and track- 
ing operation. When retro-bombs are used, the 
automatic equipment may be employed to con- 
trol their release. 


CONFIDENTIAL 


64 


MAD SIGNAL STUDIES 


The following is an excerpt from a report on 
a successful attack, illustrated by Figure 38, in 
the Straits of Gibraltar.^" 

U-Boat Contact and Attack by VP-63, 
February 24, 1944 

(a) Time — 15:59. 

(b) Own Course — 171° True. 

(c) Own Speed — 100 knots. 

(d) Altitude — 100'. 

(e) Sub Course — 120 (m). 

(f) Sub Speed — 2-2t4 knots (estimated). 

(g) Contact made by MAD on routine mission. 

(h) MAD operator fired first flare. 

(i) Second contact established by use of VP-63 spiral 
tactics. 

(j) Number of signals obtained by plane No. 14-11. 
Number of signals obtained by plane No. 15-10. 

(k) Maximum signal obtained — 40 gamma. 

(l) Minimum signal obtained — 4 gamma. 

(m) Average signal obtained — 10.5 gamma. 

(n) Average duration of signals — 7.2 seconds. 

The original contact was made by MAD at 35° 56' N — 
05° 47' W by PBY No. 15. Two smoke lights were fired 
on original contact. After three lights had been laid in 


clover-leaf pattern, PBY No. 14 joined in tracking 180° 
relative to plane No. 15. 

Contact persisted on track approximately 120° N at 
a speed of approximately 2-2V2 knots. No. 15 was within 
magnetic field on each clover-leaf pass. After 5 lights 
had been laid by plane No. 15, a British DD made a run 
down the line of float lights fouling area of MAD con- 
tact. The DD planned to attack but lost contact. After 
the DD passed through, magnetic contact could not be 
reestablished — time approximately 16:22. A search was 
started using the clover-leaf procedure. When no con- 
tacts were made, a spiral was started by plane No. 15, 
plane No. 14 continuing clover-leaf s. 

On fourth turn of spiral, contact was reestablished 
by plane No. 15 approximately IV 2 miles southeast of 
point of losing original contact. Clover-leaf tracking 
followed — plane No. 14 joining as soon as plane No. 15 
had positive contact. The pilot of plane No. 15 went in 
on bombing run, bombed at 16:55 — position 35° 55' N 
— 05° 47' W. (Three sticks of 8 — 23 bombs firing.) 
Plane No. 14 was approximately 300 yards behind plane 
No. 15. The DD fired Y gun pattern of approximately 
10 depth charges, thirty seconds after No. 14’s attack. 
DD’s depth charges exploded at 16:58. 

No. 15 circled area and at 17 :02 observed U/B break- 
ing water — leading edge of conning tower first, then 
bow, then decks awash. After hanging on the bow for 
approximately two minutes, the U/B sank — stern first. 


CONFIDENTIAL 


Chapter 5 

AUTOMATIC FIRING SYSTEMS 


O NE OF THE IMPORTANT problems concerning 
the use of the AN/ASQ-1 equipment is that 
of releasing ordnance to destroy an invisible 
target such as a submerged submarine. Hand 
firing after an indication is noted on the meters 
obviously can be inaccurate, since the time of 
reaction for different operators may vary con- 
siderably. Flying at 140 knots an airplane trav- 
els 237 feet in one second. During the fall and 
winter of 1942-1943 several equipments for the 
mechanical release of ordnance were developed. 

The production model of a tripper circuit to 
be attached to a single AN/ASQ-1 system for 
automatic release of bombs or flares upon pass- 
ing over a signal peak is called the CP-2/ASQ-1. 
It will be described later in the chapter. 


- 1 THE AN/ASQ-2 DUAL AUTOMATIC 
SYSTEM^ 

^ Principles of Operation 

Eventually the device was adopted of using 
two complete MAD systems located as far apart 
laterally as possible, at the wing tips of an air- 
plane or on opposite sides of a blimp. As indi- 
cated by the sum and difference contour charts 
of Chapter 4, the peaks of the sum of the two 
signals will usually lie close to the submarine 
and so are useful for actuating a tripper for the 
automatic release of flares or bombs. (A delay 
circuit was included in the production system 
so that the ordnance might be fired at some 
selected time after the sum peak if desired. 
This was to allow for such situations as pic- 
tured in Figure 30 of Chapter 4.) 

The difference of the two signals changes 
sign, depending on whether the aircraft is to 
the right or the left of the sum peak, and is 
therefore a useful guide to the pilot during 
combat maneuvers. In the field models the dif- 
ference signal was displayed on a right-left 
indicator microammeter. 

^ Some work was also done by the Naval Ordnance 
Laboratory on the use of dual AN/ASQ-3 systems. ^ 


During the development work various 
schemes were tried for compounding the two 
signals in such a way as to obtain a quantity 
whose value at a peak would be independent of 
the submarine moment, independent of the rela- 
tive heading of submarine and aircraft, and 
independent of the aircraft elevation, but which 
would always be a measure of the lateral dis- 
tance between aircraft and submarine. The 
variety of the possible combat situations illus- 
trated in Chapter 4 indicates that this is a 
problem of considerable difficulty. Some use was 
made of the ratio of the sum to the difference 
of the two signals.^ Clearly the anomaly field 
intensity at any point is proportional to the 
magnitude of the resultant submarine moment, 
so that in a ratio of any two linear combina- 
tions of signals this factor will cancel, leaving a 
quantity independent of the size of the sub- 
marine moment. However the other variables 
are not so easily dismissed.^ 

The system finally chosen was based on a 
statistical study^"^ of the model signals described 
in Chapter 4 and was designed to meet the re- 
quirements listed above in a high percentage 
of the cases likely to arise in combat. The 
circuit allows the tripper to release a bomb on 
a sum-signal peak only if the ratio of the two 
signals falls within certain limits. The follow- 
ing inequality must be satisfied: 

1 — A ^ E 2 I A 

fta f 1 

and both and E., must have the same sign. 
No bombs will be dropped if the two signals 
have opposite signs. The factor A may be 
varied between zero and one by a rheostat 
called the “lateral range” control. 

With 50 feet spacing between the detector 
elements, with the airship flying 200 feet above 
the submarine at 40 knots, and with the lateral 
range control set at its point 2 on the control 
panel, the statistical study indicates that the 
circuit in most situations will restrict the bomb 
release to a band whose average width is about 
100 feet. 


CONFIDENTIAL 


65 


66 


AUTOMATIC FIRING SYSTEMS 


Whenever the bombing criteria are not sat- 
isfied the tripper circuit merely releases a flare 
on the sum peak — or at an adjustable delay 
time thereafter. 

The tripper should not respond to the maxi- 
mum of every accidental peak in the back- 



Figure 1. The CM-2/ASQ-2B lateral indicator 
and automatic tripper for use in lighter-than-air 
craft. 


ground noise ; therefore the circuit is arranged 
to fire on only those peaks whose maximum is 
above a certain threshold value adjustable from 
the control panel. It is also undesirable for the 
tripper to operate on those large peaks which 
are of geological origin or are due to violent 
fluctuations in the aircraft power supply, of 
the type seen in Figures 32 and 33 of Chapter 4. 
Since a true submarine signal usually has a 
rather distinctive shape, its harmonic analysis 
will usually contain a different band of fre- 
quencies from that of a spurious signal. The 
tripper circuit contains filters which discrimi- 
nate against frequencies other than those to 
be expected from a submarine signal. 

The complete dual automatic system is known 
as AN/ASQ-2. It consists of two AN/ASQ-1 
or lA units, the auxiliary unit for compound- 
ing the signals and tripping the ordnance as 
above described, and a test signal generator 
which will be taken up in Section 5.1.3. Two 
types of the auxiliary unit were made with 
different reaction times and frequency charac- 
teristics for use in lighter-than-air and heavier- 


than-air craft, respectively. The LTA unit is 
described in the next sections. 

^ The CM-2/ASQ-2B Lateral Indicator 
and Automatic Tripper for Airships 

The CM-2/ASQ-2B unit is shown in Figure 1. 
Figure 2 is a block diagram of its functions. 
The outputs of the two AN/ASQ-1 or lA units 
(taken from the V106 plate circuits as usual) 
are fed to a balanced bridge which compounds 
their sum. This sum signal is sent, through a 
one-stage sum meter amplifying circuit, to the 
sum meter which is the usual Esterline-Angus 
recording milliammeter. Those recorders nor- 
mally connected to the AM-l/ASQ-1 units are 
replaced by this one. The sum signal is also sent 
to the tripper circuit which releases either a 
bomb or a flare or both. 

The AM-1 outputs are also sent to a bridge 
which responds to their difference. The sum 
signal and the difference signal then pass to a 
so-called ratio bridge. The output of this bridge 



Figure 2. Block diagram of CM-2/ASQ-2B. 


is fed through the lateral control circuit in such 
a way that the lateral control will not allow the 
tripper to release a bomb on a sum-signal peak 


CONFIDENTIAL 




THE AN/ASQ.2 DUAL AUTOMATIC SYSTEM 


67 


unless one of the relations previously listed is 
satisfied. The AM-1 outputs are also sent to a 
lateral indicator circuit which is essentially an- 
other difference-taking device. The detailed de- 


the input signals.'’ R705, R706, R707, and R708 
are 0.2-megohm resistors carefully matched to 
within ± 2 per cent which form the four arms 
of the sum bridge. The bridging arm is formed 



TO LATERAL 
INDICATOR 
CIRCUIT 


Figure 3. The bridge circuits and sum meter circuit of CM-2/ASQ-2B. 


scription of CM-2/ASQ-2B will be begun with 
the bridge circuits. 

The Bridge Circuits and the 
Sum Meter Circuit 

Figure 3 is a schematic wiring diagram of 
these sections of the unit together with the last 
stages of the two AM-l/ASQ-1 circuits to which 
it is attached. Resistor R712 is used to balance 


by the parallel combination of the V721 input 
resistors, the tripper input impedance, and the 
resistance of the ratio bridge section. (For pur- 

^ The requirements are rather strict on equality of 
phase response for the two AM-1 units to be attached 
to this circuit. For measurements of the phase shifts 
produced by AM-1 at various signal frequencies, see 
reference 6. The requirements on stability of the sen- 
sitivities of the two units also placed added demands on 
the production and inspection regimes.'^-^ 


CONFIDENTIAL 



68 


AUTOMATIC FIRING SYSTEMS 


poses of reference let us call input signal 
positive if terminal 9 is at higher potential 
than terminal 10, and call E.^ positive if terminal 
7 is at higher potential than terminal 8.) Posi- 
tive pulses from both detectors cause currents 


R 


R 


E 


AAA^ 


AAAr 




AAV 


AW 


R R 

Figure 4. Battery circuit equivalent to sum 
bridge. 


E2 


through the bridging arm in the same direction. 
The net voltage across the arm will therefore 
be proportional to the algebraic sum of the 
two signals. The effect is the same as that in 
the simple battery circuit of Figure 4 where 
the voltage across the bridging arm S is easily 
shown to be 


Vs = 


S 

R S 



The sum signal actuates the recorder through 
the V721 stage in the usual manner. 

The difference bridge is so connected that 
pulses of the same polarity from the two de- 
tectors cause currents in opposite directions 



Figure 5. Battery circuit equivalent to ratio 
bridge. 


through the bridging arm. The voltage across 
the arm, is then proportional to the alge- 
braic difference between the signals. 


As shown in Figure 3 the difference voltage 
is fed directly to the ratio bridge. The sum 
voltage is attenuated by an adjustable factor A 
with the potentiometer R721, R722, R723. The 
voltages applied to the ratio bridge are then 
Vd and AVs. In the absence of signal all points 
of the three bridge networks rest at the po- 
tential, Vj^, of the points K in the AM-1 cir- 
cuits, which is about +260 volts. Any signal 
voltages will cause the potentials of points E 
and F on the ratio bridge arms to rise or fall. 

The polarity and magnitude of the voltage 
changes at E and F, which may be called 
and AF^, can be understood by comparison 
with the battery circuit of Figure 5. Solution of 
the elementary equations of this circuit gives 
for the potential differences between E and K, 
and F and K: 


Ve - Fx 


AFs - Vn 
4 


Vf - Vk = - 

Since the potential of E and F is F/c in the absence 
of signal (Fs = Vd = 0), the above expressions 
represent the voltage changes AV e and AV f re- 
quired. If both input signals, Ei and E 2 , are 
positive, then the potential of E will rise and that 
of F will fall. Other combinations of input signals 
will cause different behavior. The explicit de- 
pendence of AF^; and AV f on Ei and E 2 is given 
by substituting in the values of F^ and V d’- 


5+ = EAI+ A) - E, (1 - A) 


8AFp 

= E, {I - A) - E, (1 + A). 

The extra attenuation factor B has been added 
to allow for the effects of the finite impedance of 
the sum and difference bridges. The effect of 
these voltage changes on the lateral control 
circuit is taken up in the next section. 

The Lateral Control Circuit 

Figure 6 is a schematic diagram of the lateral 
control section of CM-2/ASQ-2B. It is a dual 
three-stage amplifier which includes several 
filter networks. A rise in the potential of E 
causes a transient input signal voltage across 


CONFIDENTIAL 


THE AN/ASQ-2 DUAL AUTOMATIC SYSTEM 


69 


R799 which is amplified through the circuit so 
as to cause an increase in the V714 cathode 
current flowing through the relay K703. In 
the absence of signal, V714 is biased almost to 
cutoff and so K703 is open. If AF^ is positive 
and greater than some fixed amount, e volts, 
then the output* current will be sufficient to 
close relay K703. 

Similarly, if AF^is positive and greater than 
e volts the relay K704 will close. Now the points 
I and J are so connected in the tripper circuit 


The terms involving e will always be small. For 
example : 


4e {R + 1) 
BEiR 


< 0.08, 


since B > 0.5, e 10 millivolts, Ei > 2 volts, 
and (R + 1)/R < 2, (since /? > 1). Neglecting 
these terms gives the approximate condition 
for bombing: 


1 — A ^ E 2 ^1+A 
1+A^ Ell - A’ 



Figure 6. The lateral control circuit of CM-2/ASQ-2B. 


(to be described in a following section) that a 
bomb cannot be released unless there is a closed 
circuit in the lateral control from I to J. But 
the circuit from 7 to / will be closed if either 
K703 or K704 closes but not if both or neither 
of them close. One circumstance which will 
allow the release of a bomb is, then, AF^ >e and 
simultaneously AF^ <e. The other case is for 
AF^, >e and AF^ <e. Substitution of the for- 
mulas derived above for AF^ and AF^ leads to 
the following inequality : 


1 - A 86 ^ F 2 

1 + A R (1 + A) Fi 


1 “h A 86 

1 “^^ R (1 - A) Ef 


provided and E^ have the same sign. If 
E^ and E^ have opposite signs, the conditions 
cannot be satisfied. 

This equation may be simplified by substitut- 
ing R — (1 + A)/(l — ,:4)» to give 


1 / 46 (R A- 1) \ 

R \ BEi ) 




46 (R + 1)\ 
BEiR ) ' 


with E^ and E^ having the same sign at a peak. 
As seen from this formula, increasing A in- 
creases the allowed lateral bombing range. 

The Tripper Circuit in CM-2/ASQ-2B 

The functions which the tripper circuiU^'^^ 
performs are the following. 

1. It rejects sum signals under a certain ad- 
justable threshold magnitude. 

2. It rejects sum signals whose chief fre- 
quency components are either too high or too 
low. 

3. For all sum signals which are not re- 
jected because of small size or improper fre- 
quency, it closes an external flare-dropping cir- 
cuit at an adjustable time after a sum signal 
voltage peak of either polarity. 

4. If the lateral control circuit indicates that 
bombs should be dropped, it also closes a bomb- 
dropping circuit at the same time that the 
flare-dropping circuit is closed. 

A block diagram of this circuit is given in 
Figure 7. A brief and general description of the 


CONFIDENTIAL 


70 


AUTOMATIC FIRING SYSTEMS 


functions of the various stages will first be 
given, to be followed by a detailed discussion of 
the operation of each stage. 

The first stage, which is an amplifier of ad- 
justable overall gain, performs the first function 
listed above. Eventually, at the sixth stage, the 
signal is required to exceed a certain magni- 



FROM AIRCRAFT 


BOMB SAFETY CIRCUIT 

Figure 7. Block diagram of tripper circuit in 

CM-2/ASQ-2B. 

tude. Hence, adjustment of the gain of the first 
stage controls the firing threshold. 

The second stage, a rectifier, is required to 
enable the tripper to operate on signal voltage 
peaks of either polarity. 

The third stage, a filter and rectifier stage, 
performs the chief part of the second function 
listed above; viz., that of rejecting signals hav- 
ing frequency components which are either too 
high or too low. 

The fourth stage is merely an impedance 
transformer required to obtain a low driving 
impedance for the following stage. 

The function of the fifth stage, called the 
electronic switch, is to produce a short voltage 
pulse as soon as possible after the occurrence 
of a signal voltage peak of either polarity. It 


is this pulse which actuates the firing circuits. 
Thus, the signal peak is the index point for fiare 
or bomb dropping. 

The sixth stage is a relay stage which starts 
the time delay circuits of the flare dropper and 
also passes a firing pulse to the eighth stage. 

The seventh stage controls the adjustable 
time delay for the flare dropping mentioned as 
part of the third general function above. 

The eighth stage is a relay stage which starts 
the bomb time delay circuit upon receipt of the 
firing pulse from the sixth stage, provided the 
lateral control circuit indicates that bombing 
should occur. 

The ninth stage corresponds to the seventh 
stage and is always adjusted to the same delay 
time by a ganged control. 

The reader may well wonder at the multi- 
plicity of stages required to perform the four 
functions originally listed. This circuit com- 
plexity was arrived at rather empirically and 
was found to give the greatest possible freedom 
from malfunction while possessing the desired 
characteristics. 

A detailed description of the operation of 
the various stages is now given. 

First Stage: Amplifier. The first stage is a 
class A push-pull amplifier, as shown in the 
schematic diagram of Figure 8, which also 
shows the input and output wave forms. The 
input signal comes from the points 1 and 2 
of the sum bridge. Potentiometer R726 serves 
as a threshold control. The time constant of 



the coupling circuit is from 10 to 11 seconds, 
and the impedance is sufficiently high so that 
it will not load the output stage of the AM-1/ 
ASQ-1 units enough to cause appreciable dis- 
tortion. The voltage gain of this stage is about 


CONFIDENTIAL 


THE AN/ASQ-2 DUAL AUTOMATIC SYSTEM 


71 


60, and the maximum undistorted output from 
plate to plate is about 200 volts. 

Second Stage: Rectifier. The second stage is 
a cathode follower which acts as a rectifier. 
Its input circuit is a high-pass filter with a 
10-second time constant which prevents distor- 
tion of the signal. A 12SL7 tube is biased be- 
yond cutoff and is unresponsive to small noise 
voltages. Since the grids have opposite polarity 
at any instant of a signal, only one section of 
the tube conducts at a time; and, since the 
outputs are in parallel, the output signal is 
rectified. This stage can accept signals up to 
about 150 volts without distortion. A diagram 
of this stage, including the output-signal form 


V-702 



f300 V 
© 


Figure 9. Second stage of tripper: rectifier. 

is shown in Figure 9. (In these diagrams the 
sources of bias voltages are shown as batteries 
instead of the potential dividers actually used.) 

Third Stage: Filter and Rectifier. The next 
part of the circuit, shown in Figure 10, dis- 



Figure 10. Third stage of tripper: filter and 
rectifier. 

criminates against high- and low-frequency 
voltages^^ and provides a voltage difference at 
signal frequencies for operating the remaining 
tripper circuit. The input voltage at points 9 
and 10 is the rectified output of the second 
stage. At very high frequencies, the reactances 


of the capacitors are negligible compared to 
the resistances of R739 and R740. Hence, equal 
voltages will appear at points 11 and 12, and 
the net output voltage will be very small. At 
very low frequencies, the reactances of the 
capacitors are so great that voltages appearing 
at points 11 and 12 will be very small. How- 
ever, at signal frequencies, a larger voltage will 
appear at 12 than at 11, since the time constant 
for the path to 12 is twice that for the path to 
11. (Since these time constants are too small 
to prevent the signal from passing without 
distortion, the voltages at 11 and 12 will become 
negative during some part of the signal dura- 
tion because of the derivative-taking action of 
the circuit.) 

The frequency-discriminating network is 
part of the third stage which is also shown in 
Figure 10. This stage consists of a 6H6 diode 
limiter. Whenever a negative voltage appears 
at 11 or 12, the diodes conduct so that the 
voltages appearing at 13 and 14 never become 
negative. This rectification is essential for cor- 
rect operation of the following stages. The 
form of the voltages at 13 and 14 is shown in 
the diagram. The peak at 14 is delayed with 
reference to the peak at 13. 


V-704 



Figure 11. Fourth stage of tripper: impedance 
transformer. 


Fourth stage: Impedance Transformer. This 
stage, shown in Figure 11, is a cathode fol- 
lower which can accept signals of as much as 
100 volts without distortion. It is an impedance- 


CONFIDENTIAL 


72 


AUTOMATIC FIRING SYSTEMS 


matching device which provides a high im- 
pedance for the preceding stage and a low 
impedance for the following stage. 

Fifth Stage: Electronic Switch. A schematic 
diagram of the fifth stage is shown in Figure 
12A while 12B is an equivalent circuit diagram 


" — ] ^ r~ 

\ 0.50 MF _L V-705 

F \ J ^ ~5 

V 1 2.0 M 

Eo 

< V-704 f 

1 



i 


A EQUIVALENT CIRCUIT FOR 1^2 OF FOURTH AND FIFTH STAGES 




Figure 12. Fifth stage of tripper: electronic 
switch. 


to be closed and the current to charge the ca- 
pacitor. The drop in V705, which is the output 
Eq, has remained at a small positive value 
throughout this quarter cycle as indicated by 
line ah in Figure 12C. 

During the second part of the signal cycle 
the voltage Ex is decreasing from a positive 
maximum value to zero. The current, however, 
increases from zero in the opposite direction, 
opening the electron switch, and flowing 
through the 2-megohm resistor R745. The im- 
portance of this change in the path of the cur- 
rent is that the time constant of the circuit 
has been greatly increased by it, and that the 
output voltage E'o is now a result of the nega- 
tive voltage drop across the 2-megohm resistor, 
line he, Figure 12C. When E-^ has reached 
zero, a maximum negative current flow has 
produced a maximum negative value for Eo. 
Because the RC value of the discharge circuit 
is longer than that of the charging circuit, 
there is a certain charge left in the capacitor 
at the time Ex reaches zero. Therefore, since 
Ex remains at zero for an interval, this charge 
will leak off through R745, reducing E^ ex- 
ponentially, line cd, Figure 12C. It should be 
remembered that the equivalent circuit diagram 
during this interval reduces to a resistor con- 
nected across a capacitor, since E^ may be 
disregarded while it remains zero. When Ex 


of one-half of the fourth and fifth stages. This 
diagram demonstrates the combined action of 
these stages in modifying the output-signal 
form of the third stage, shown in Figure 10, 
to the form shown in Figure 12C as the output 
of the fifth stage. 

Since the fourth stage, a cathode follower, 
does not modify the wave form but functions 
simply as an impedance-matching device, it 
may be represented in Figure 12A as a low- 
impedance voltage source producing the signal 
voltage E^. Also, V705 may be represented as 
an electronic switch, closed or conducting when 
the plate is slightly positive to the cathode and 
open when this slight positive potential is re- 
moved. 

For the first part of the signal cycle, the 
voltage E^ is positive and increasing, which is 
the necessary condition for the electron switch 



Figure 13. Sixth stage of tripper: relay. 


again increases from zero in a positive direc- 
tion, Eo will follow until such time as the 
electron switch operates again. 

The schematic diagram shows that the fifth 
stage is composed of two channels with differ- 


CONFIDENTIAL 


THE AN/ASQ-2 DUAL AUTOMATIC SYSTEM 


73 


ent input voltages which are similar to the 
output voltages at points 13 and 14, Figure 11. 
Therefore, the output voltage at 17 will reach 
its maximum negative value (c') ahead of the 
output voltage at 18 (c). This can be seen in 
Figure 12C by. comparing curve ahcd with 
abc'd\ 

Battery B701 does not affect this stage ap- 
preciably but is used as a bias in the next stage. 

Sixth Stage: Relay. The voltage at point 17 
is applied to the grid of V706, while the voltage 
at point 18 is applied to the cathode of the same 
tube as shown in Figure 13. The bias battery 
makes the grid about 6 volts negative with 
respect to the cathode. When the negative sig- 
nals are impressed, the grid becomes positive 
with respect to the cathode. If this difference 
voltage is enough to overcome the grid bias, 
the tube will “fire,’' but this depends upon the 
difference in peak values of the grid and 
cathode voltages, the time interval between the 
peak of the grid signal and the peak of the 
cathode signal, and the positive grid increment 
caused by the discharge of C709 during the 
time interval mentioned above. If the tube 
fires, it must do so during this interval, for 
after it the difference voltage decreases in 
magnitude. The difference voltage is approxi- 
mately proportional to the signal amplitude as 
long as the capacitor, resistor, and bias values 
of this part of the circuit remain fixed. There- 
fore, the operator can determine the size of 

R-752 


R-753 




Figure 14. Seventh stage of tripper: time delay. 

signal necessary to fire the V707 by the thresh- 
old setting of the first stage. 

The diode part of V707 is in the cathode 
circuit of V706. Its purpose is to isolate the 
cathode of the thyratron until the 2050 fires. 


When this occurs, the cathode becomes positive 
enough to overcome the 3-volt diode bias which 
then allows the diode to conduct, and the voltage 
developed across resistor R749 is used as the 



output voltage. Points 19 and 20 are the input 
terminals of the next stage, while point 21 is 
the input terminal of the eighth stage. 

Seventh Stage: Time Delay. The last stage 
of the flare-release circuit is shown in Figure 
14. The output signal from the preceding stage 
charges capacitor C712 through delay resistor 
R752. The value of this resistor determines 
the delay setting or time necessary for the 
capacitor to charge to the specific voltage re- 
quired for V708 to conduct. When the latter 
conducts, it discharges C712 and charges C713 
in a direction such that the grid of V707 be- 
comes positive and the triode conducts. When 
this occurs, enough current, which must be 
more than 1.4 ma, flows through the plate cir- 
cuit to operate relay K701. The contacts shown 
in Figure 13 open, thereby extinguishing V706, 
and the contacts shown in Figure 14 close, 
thereby operating the flare circuit shown in 
Figure 15. 

By the time the triode has stopped conduct- 
ing, causing the relay to release, V706 has 
stopped conducting, and its grid-to-cathode 
voltage has decreased sufficiently to prevent it 
from firing again when the plate voltage is re- 
applied. 

Flare Circuit. When K701 operates, it closes 
the flare circuit shown in Figure 15. The white 
indicator lamp 1701 is in parallel with the flare 
circuit, so that it lights whenever the relay 


CONFIDENTIAL 


74 


AUTOMATIC FIRING SYSTEMS 


operates; i.e., whenever the detector crosses a 
signal peak. 

If switch S703 is closed, the circuit contain- 
ing the green indicator lamp 1702 is closed. 



If the flare-safety circuit of the aircraft be- 
tween terminals 14 and 15 is closed, then relay 
K702 will close the flare-release circuit between 




terminals 2 and A2 whenever the white and 
green lamps are lighted. 


Hand Fire Circuit. Figure 16 shows the hand 
Are circuit. When push-button switch S702 is 
closed, the circuit containing relay K702 is 
closed, and, therefore, the flare-release circuit 
is closed. Also, when the switch is closed the 
flare-safety circuit is opened. This isolates the 
flare relay and prevents the operation of the 
bomb relay by means of the hand fire switch. 



Figure 18 . Ninth stage of tripper: time delay. 


The only requirement for closing the flare- 
relay circuit by means of the push button is 
that the main ASQ power switch be on. 

Eighth Stage: Relay. The eighth stage of the 
tripper circuit is shown in Figure 17. Point 21 
is connected to the cathode of the diode section 
of V707. Therefore, the input voltage between 
21 and circuit ground, point 22, is not the modi- 
fied input signal but is a pulse that results when 



V706 fires. It is approximately a square wave 
of duration equal to the delay set by the con- 
trol. If neither of relays K703 and K704 is 
closed, and if lateral range control switch R723 
is not set on “Inf.’' (position 8 in diagram), 
then the voltage pulse at 21 will pass through 


CONFIDENTIAL 


THE AN/ASQ-2 DUAL AUTOMATIC SYSTEM 


75 


the d-c blocking capacitor and filter resistor 
R819 to ground. The R723 shown here is a 
switch mounted on the same shaft as the poten- 
tiometer R723 shown in Figure 3. If either, but 
not both, of the relays is closed or if R723 is set 
to position 8, then R819 is shorted and the sig- 
nal is applied to the voltage divider, R834 and 


voltage developed across R749 of the sixth 
stage. 

Ninth Stage: Time Delay. The last stage of 
the bomb-release circuit. Figure 18, is similar 
to the last stage of the flare-release circuit. 
The corresponding component parts of the two 
circuits perform the same functions, so that 



Figure 20. The complete tripper section of CM-2/ASQ-2B. 


R835. The pulse overcomes the 13-volt bias on 
V709, and the tube conducts. The current 
through R821 is enough to raise the voltage 
at the plate of the diode section of V710 suf- 
ficiently high to cause the diode to conduct and 
develop a voltage across R823 similar to the 


the discussion of the seventh stage applies 
equally well to this stage. The circuit operates 
relay K705, which opens the contacts shown 
in Figure 17, thereby extinguishing V709, and 
closes the contacts shown in Figure 18, thereby 
operating the circuit shown in Figure 19. 


CONFIDENTIAL 


76 


AUTOMATIC FIRING SYSTEMS 


Bomb Circuit. When K705 operates, it closes 
the bomb circuit which is similar to the flare 
circuit and is shown in Figure 19. Terminals 
23 and 24 lead to the aircraft bomb safety cir- 
cuit. 

Figure 20 is the schematic diagram of the 
complete tripper section. 


rectified. The plates are normally at -1.5 volts. 

The principal parts of the last stage are a 
shorting switch S704, two variable-mu pentodes 
V719 and V720, a meter-balancing potentiom- 
eter R790, and an output lateral-indicator meter 
M701. The input coupling circuit is a low-pass 
filter with a four-second time constant. With 



The last part of the circuit to be discussed is 
the lateral indicator, which is the subject of the 
next sections. 

The Lateral Indicator Circuit 

Figure 21 is the schematic diagram of this 
circuit. The first stage consists of two class A 
push-pull amplifiers. When switch S701 is set 
on the OPR position, one tube amplifies the 
signals from one AM-l/ASQ-1 detector, and 
the other tube amplifies the signals from the 
other detector. Rheostat R767 is called “Lat. 
Ind. BaU’ on the panel and is used to balance 
the two circuits when they have the same input 
signal if S701 is set to the position marked 
'‘Bal.” The second stage consists of two full- 
wave rectifiers, with an 11.5-volt diode bias so 
that small signals and random noise will not be 


normal signals, the voltage across the 4-|Af 
capacitors remains less than 10 per cent of the 
voltage at the diode plates. The capacitors must 
discharge through 3 megohms so that the time 
constant is well above four seconds and the 
meter assumes a deflection during the signal 
which it holds for some time after the signal 
has passed. Lateral reset switch S704 enables 
the operator to short the capacitors and return 
them to their original potential of -1.5 volts. 
This operation should be performed after every 
signal. By means of the potentiometer marked 
‘^meter balance’" on the panel, the meter can 
be adjusted to give zero indication for zero 
signal. The output current is approximately 
proportional to the logarithm of the negative 
grid voltage. Since the lateral indicator reads 
the difference of the plate currents of the two 


CONFIDENTIAL 


THE AN/ASQ-2 DUAL AUTOMATIC SYSTEM 


77 


tubes, its reading is proportional to the 
logarithm of the ratio of the negative grid 



Figure 22. The control panel of CM-2/ASQ-2B. 

voltages. The indication for a given ratio re- 
mains constant over a range of magnitude of 
input voltage of six to one, falling off to zero 


for very large and very small signals. The 
pilot’s indicating meter is to be connected be- 
tween terminals 11 and 12. 

Summary of Controls 

As a summary of the operation of the CM-2/ 
ASQ-2B lateral indicator and tripper unit the 
following list of its controls is presented. Fig- 
ure 22 is a front view of the control panel with 
the parts numbered to agree with this list. 

1. Threshold. This control has settings num- 
bered from 1 to 5, corresponding approximately 
to the five large divisions on each side of center 



Figure 24. Signal generating circuit of CU-36/ 
ASQ-2. 


of the Esterline-Angus recorder. For example, 
with threshold set at 2, the CM-2 unit will oper- 
ate the flare-release circuit whenever a signal 
occurs which causes a pen deflection greater 
than approximately two large divisions from 
center on the recorder tape and will also oper- 
ate the bomb-release circuit if the lateral con- 
trol permits. The sum meter is calibrated to 
give a full-scale deflection when each of the two 
ASQ meters gives a full-scale deflection. 

The calibration of the threshold control is 
influenced by the condition of the bias battery 
B701. This battery voltage may be changed 
over a range from 4.5 to 6 volts to correct the 
calibration. 

2. Flare switch. When this switch is set to 
the On position the flare-release circuit will be 
closed whenever a signal greater than the 
threshold amplitude occurs if the flare safety 
circuit is closed. 

3. Bomb switch. When this switch is set to 
the On position the bomb-release circuit will 
be closed whenever a signal greater than the 
threshold amplitude occurs, if the lateral con- 

oo rr 4. • 1 4. ^ ^TT / ti*ol permlts and if the bomb safety circuit is 

Figure 23. Test signal generator of CU-36/ . , 

ASQ-2. closed. 



CONFIDENTIAL 



78 


AUTOMATIC FIRING SYSTEMS 




CONFIDENTIAL 


Figure 25. Schematic circuit diagram of lateral indicator and tripper for airplanes, CM-l/ASQ-2. 


THE AN/ASQ-2 DUAL AUTOMATIC SYSTEM 


79 


4. Delay. The setting of this control de- 
termines the time interval between the peak 
of the signal and the closing of the flare- and 
bomb-release circuits. The numbers 0 to 10 
correspond approximately to zero to seven and 
a half seconds delay ; that is, each division rep- 
resents three-quarters of a second. The proper 
setting of the control depends upon the area 
of operation and may not be the same for flare 
releasing as for bomb releasing. 


circuits are adjusted by the lateral indicator 
balance control. Otherwise it is set in the 
operate position. 

9. Lat. ind. bal. With this control, the lateral 
indicator circuits in the CM-2 unit may be 
balanced. 

10. Input bal. This control is used to balance 
the outputs of the two ASQ equipments. 

11. Hand fire switch. Whenever this push- 
button switch is depressed, the flare-release 


LATERAL DISTANCE IN FEET 


$ 0 LlOO 0 100 R LlOO 0 100 R L 100 0 lOOR 


0 0 

45 



















90 

135 

180 

45 0 

45 

90 

135 

ISO 

90 0 

45 

90 

135 

180 

135 0 

45 

90 

135 

180 

180 0 

45 

90 

135 

180 








1 1 














DIP ANGLE =70“ 






b 

to 

UJ 

_l 

o 

2 

< 







DIP ANGLE = 10“ 





























Q. 

O 















LATERAL" YES" 
RANGE OF CM-I/AS 










0-2 







ALT= 2r00 FEET 

SPEED=300 FEET PER 
SEC 

$z PLANE HEADING 

0 = BEARING OF TARGET 

^ rnilDCC U/ITU DCCDC 





































TO PLANE COURSE 

Mv= Ml, M-psO 




- 






















- 

— 






























































































Figure 26. Lateral firing range of CM-l/ASQ-2 in various situations, as obtained from model signal 
studies. 


5. Lateral range. The setting of this control 
determines the lateral limit on the operation 
of the bomb-release circuit. 

6. Lat. reset switch. This switch permits 
quick reset of the lateral indicator meter to 0 
after it has been deflected by a signal. 

7. Meter balance. This adjustment is for 
initially setting the lateral indicator meter at 0. 

8. Operate bal. switch. This switch is thrown 
to the Bal. position when the lateral indicator 


circuit is closed regardless of the setting of the 
flare switch, bomb switch, threshold control, or 
of continuity in the flare safety circuit, if the 
main ASQ power switch is turned on. 

12. Sum bal. This control is used to bring 
the pen of the sum recorder to center scale 
when the CM-2 unit is initially adjusted after 
the power is turned on. 

13. Indicator lights. The CM-2 panel contains 
four pilot lamps. The green flare ready lamp 


CONFIDENTIAL 



80 


AUTOMATIC FIRING SYSTEMS 


(G) burns continuously when the flare switch 
is set to the On position. The red bomb ready 
lamp (R) burns continuously when the bomb 
switch is set to the On position. The white flare 
relay (W) burns for about five seconds every 
time a signal greater than threshold amplitude 
occurs, regardless of the positions of the bomb 
and flare switches. The lighting of this lamp 
indicates that the sensitive relay, K701, has 
closed and that a flare will be released if the 


circuit is closed. Bomb and flare switches must 
not be turned from off to on while relay lamps 
are lighted since this will cause bombs and 
flares to be released. 

^ Test Signal Generator 

This unit, which is shown in Figure 23, is a 
part of the standard AN/ASQ-2 dual installa- 
tion. It contains (1) a switch which enables 
the operator to connect the recording meter 


LATERAL DISTANCE IN FEET* 



flare switch is On and the flare safety circuit 
is closed. The amber bomb relay lamp (A) 
burns for about five seconds every time a signal 
greater than threshold amplitude occurs, re- 
gardless of the positions of the bomb and flare 
switches, providing that the target is within 
the lateral range determined by the setting of 
the lateral range control. The lighting of this 
lamp indicates that the sensitive relay, K705, 
has closed and that a bomb will be released if 
the bomb switch is on and the bomb safety 


either to the port detector, to the starboard 
detector, or to the sum meter circuit of the 
CM-2 unit; (2) a switch which enables the op- 
erator to turn the pilot’s remote meter on or 
off; and (3) a push-button switch which en- 
ables the operator to produce a signal which 
can be used to balance the two ASQ sets and 
the CM-2 unit. Figure 24 is a diagram of the 
signal generating circuit. A more elaborate 
signal generator, called TS-160/ASQ-2, was 
also used in laboratory testing of CM-2 units. 


CONFIDENTIAL 



THE AN/ASQ.2 DUAL AUTOMATIC SYSTEM 


81 


5.1.4 Lateral Indicator and 

Tripper for Airplanes 

As mentioned earlier in this chapter, a 
separate lateral indicator and tripper unit 
similar to CM-2 was constructed for use in 



Figure 28. Automatic tripper for single MAD 
systems, CP-2/ASQ-1. 


heavier-than-air installations. Its circuit con- 
stants were adjusted to the higher range of 
signal frequencies to be expected from detectors 
carried in airplanes instead of blimps and to 
the greater lateral separation of the two mag- 
netometer heads possible on the airplane. Other- 
wise its construction and operation were identi- 
cal to the CM-2. This unit was labeled CM-1/ 
ASQ-2; its circuit diagram is given in Fig- 
ure 25. 

5.1.5 Performance Characteristics of 
the Dual Automatic System 

Very little actual operating experience with 
these dual systems was obtained during the 
war.i^'^^* A number of model signal studies were 
made, from which Figures 26 and 27 show 
some results. The indications are that while the 
system is workable it cannot be expected to 
fire correctly every time, because of the broad 
range of the field variables which may occur in 
combat. 



Figure 29. Circuit diagram for CP-2/ASQ-1 tripper. 
CONFIDENTIAL 



82 


AUTOMATIC FIRING SYSTEMS 


-2 AUTOMATIC TRIPPER FOR SINGLE 
MAD SYSTEMS 

As stated at the beginning of this chapter, 
a tripper unit was also built for automatic re- 
lease of retro-fired ordnance at the peak of a 
single MAD signal. A number of these were put 


in service. The unit,^^ called CP-2/ASQ-1, is 
shown in Figure 28, and its schematic wiring 
diagram is given in Figure 29. The circuit and 
its method of operation are practically identical . 
with the tripper section of CM-2 already de- 
scribed — except, of course, for the absence of 
the lateral control restriction on bomb release. 


CONFIDENTIAL 


Chapter 6 

INSTALLATIONS OF MAD IN AIRCRAFT 


W HEN THE MAGNETIC detector of an ASQ in- 
stallation is located near, or fastened to, 
the aircraft, spurious indications are usually 
recorded during maneuvers, of which Figure 1 
is a sample. These indications are caused by 
the presence of (1) permanent and (2) induced 
magnetic fields at the detector which arise from 
ferromagnetic members of the aircraft and (3) 
magnetic fields set up by eddy currents gener- 
ated in the conducting sheets and structures 
of the aircraft by the maneuvers.^ If such in- 



Figure 1. Maneuver noise from 360-degree turn 
in uncompensated plane. 

dications are large, they may mask the signal 
from the target. Two methods of attack on this 
problem suggest themselves. One is to remove 
the magnetometer head from the plane and tow 
it behind in a suitable housing attached to the 
plane by a long cable. This method of the '‘towed 
bird” was carried out successfully in several 
laboratory installations but did not reach the 
field during the war. It will be discussed in Sec- 
tion 6.2. The method which has actually been 
used in service so far is to locate the head in 
the quietest possible position on the aircraft 
and then to compensate for any remaining 
troublesome ambient fields with properly placed 

^ Of course the magnetometer head itself must have 
been carefully designed to avoid maneuver noise due to 
ferromagnetic parts and eddy-current loops in the 
gimbals. 1 


permanent magnets or other devices. This com- 
pensation technique is the subject of the next 
sections. 


COMPENSATION OF MAGNETIC 

FIELDS IN MAD-EQUIPPED AIRCRAFT*’ 

Only permanent magnetic fields were com- 
pensated at first, as induced and eddy-current 
effects appeared to present problems of too 
great complexity for the practical application 
of compensation procedures. In spite of this, 
analytical work was carried on with the hope 
that the disturbing fields in actual aircraft 
would be simpler than in the general case in 
which all components of the fields are assumed 
to be present. 

Field work carried on concurrently with 
laboratory experiments showed that the greater 
part of the disturbing field is usually of a rela- 
tively simple character. It was found possible 
to completely compensate installations which 
involve the most complex magnetic fields be- 
cause of the iron in the aircraft, provided the 
eddy-current effect is sufficiently simple in form. 
If the compensation is carried out at a single 
dip angle, the separation of some of the mag- 
netic components is difficult. It may become 
necessary to adjust the compensation if the air- 
craft is flown to a location where the dip angle 
is more than 30° greater or less than that at 
which compensation was effected. In medium 
latitudes this may not be necessary, but for 
other locations it appears that the readjustment 
cannot be avoided if particular components are 
present. If the compensation procedure is 
carried out for an installation once at a high 
dip angle and again at a low dip angle, a single 
set of compensating factors can be found which 
will be valid for all latitudes. 

The disturbing magnetic fields may be com- 
pensated by the use of either electronic or non- 
electronic devices. Both have been successfully 

b For a more detailed discussion see references 
2 and 3. 


CONFIDENTIAL 


83 



84 


INSTALLATIONS OF MAD IN AIRCRAFT 


used in practice, and each method has certain 
advantages which must be weighed against 
the disadvantages for each installation. Permal- 
loy strips and copper rings, used for nonelec- 
tronic compensation, usually extend outside the 
housing of the detector head and are objection- 
able from the standpoint of aerodynamics. 
However, Figure 2 illustrates a successful in- 
stallation of copper rings. The use of electronic 



Figure 2. Copper rings installed outside stream- 
lined housing. 


devices increases the cost and the weight of 
the installation and reduces the reliability of 
operation. In general, it can be said that elec- 
tronic compensating devices should be used only 
when an installation cannot satisfactorily be 
adapted to nonelectronic compensation. 


^ ^ ^ Location of the MAD Head on 
the Aircraft 

The difficulty encountered in the compensa- 
tion of the disturbing fields in an aircraft 


depends more upon the complexity of the field 
geometry than upon the magnitude of the re- 
sultant indications. The most complex magnetic 
fields require the greatest amount of prelimi- 
nary work in the analysis of the fields and the 
most complete compensating equipment. Con- 
sequently, the detector should be located in such 
a position that the complexity of the magnetic 
fields is minimized. 

The MAD head must be placed in the aircraft 
in a position which is most favorable from the 
magnetic standpoint regardless of installation 
difficulties. For instance, the instrument may be 
less accessible for servicing, and the support 
for the housing may need to be heavier or may 
have undesirable aerodynamic properties. How- 
ever, all such considerations should be sub- 
ordinate to the primary objective of placing 
the head in the position where the equipment 
may function most effectively. 

The installation of a single detector in an 
aircraft allows considerable latitude in the 
choice of its location. The head may be at- 
tached to any favorable portion of the wing 
(Figures 3 to 5) and is sometimes installed 
at the tail of the aircraft (Figures 6 and 7) to 
remove it as far as possible from disturbing 
parts such as the engine and the landing gear. 
On a blimp the head is usually placed in a 
blister (Figure 8). If a dual installation is to 
be made, there is little choice as to the general 
location of the detectors since they must be 
placed near the wing tips of an airplane to at- 
tain maximum separation between them. When 
a tentative location has been selected, an idea 
of the magnetic field at that point should be 
obtained. Construction diagrams of the air- 
craft will show the geometry of the ferro- 
magnetic parts and will make possible a fair 
estimate of the types and magnitudes of the 
magnetic terms. Ground measurements can be 
used to great advantage in the choice of a 
favorable location. 

When a detector is attached to the wing of 
an airplane, it is generally supported by a fair- 
ing in order to place it at some distance from 
the wing surfaces and struts. In this way, the 
effect of eddy currents is minimized. Regarding 
the effect of eddy currents, sufficient informa- 
tion is not available to permit specifying the 


CONFIDENTIAL 


COMPENSATION OF MAGNETIC FIELDS 


85 



Figure 3. Installation on TBF wing tip. 


Figure 4. Installation on PBM wing tip, AN/ 
ASQ-2A Starboard DT-3 unit. 





Figure 5. Installation on wing of PBY-5A. 


Figure 6. A tail cone installation. 



i 


Figure 7. Close-up of PBY tail cone. 


Figure 8. MAD blister on K-type blimp. 



CONFIDENTIAL 



86 


INSTALLATIONS OF MAD IN AIRCRAFT 


amount of separation of the detector from the 
disturbing surface which would make the eddy- 
current effect negligible for a particular in- 
stallation. In a typical wing-tip installation for 
a large airplane (PBM-3C) a location of the 
head 3 feet above the tip of the wing gave sat- 
isfactory results. If the head were mounted 



Figure 9. Eddy currents from PBY wing tip, 

7 feet, 9 inches inboard. 

over the main section of the wing, a different 
separation would probably be necessary. The 
head can also be mounted forward of the lead- 
ing edge of the wing. Figure 9 shows the mag- 
nitude of the eddy-current effect as a function 
of the distance forward of the leading edge of 
a PBY-5 wing, 7 feet inboard. 

Magnetic Components of the 
Disturbing Fields 

Permanent and Induced Fields — 

Analysis^'® 

The permanent field is independent of the 
attitude of the airplane with respect to the 
magnetic field of the earth. The induced field 
is a function of the attitude of the airplane. 

It is convenient to resolve any disturbing 


field at the head into three mutually perpen- 
dicular components parallel to the natural axes 
of rotation of the aircraft. The longitudinal 
component is parallel to the fore-aft axis of 
the aircraft and is positive forward. The trans- 
verse component is athwartship and is positive 
to port. The vertical is positive downward. 

The perm components along these directions 
are designated as L, T, and V. The permanent 
magnetic field resulting from any part of the 
aircraft may be represented by a set of three 
permanent magnets, giving the appropriate 
field at the detector in the L, T, and V direc- 
tions. 

The induced' magnetic field from any part 
of the aircraft is equivalent to that of a set of 
three magnets parallel to the L, T, and V axes. 
The combined effect of all the parts can be 



Figure 10. Adjustable perm compensator mag- 
nets installed in a PBY wing. 

replaced, therefore, by three soft iron bars 
which are parallel to, but not on, the L, T, and 
V axes. Each of these bars produces at the 
head a field having components in all three di- 
rections. Thus, the total field at the detector 
in the L direction is equal to the sum of the 
L component from the bar situated in the L 
direction, and the L components from the T 
and V bars. 


CONFIDENTIAL 



COMPENSATION OF MAGNETIC FIELDS 


87 


The components of induced magnetism are 
complicated, since the relationship between the 
components changes as the airplane changes 
position in the earth’s field. A convenient 
double-letter notation has been adopted to des- 
ignate induced fields at the detector. The first 



Figure 11. Deperming equipment. 


letter stands for the direction of the source, 
and the second stands for the direction of the 
component of the magnetic field at the detector 
due to that source. Since the magnitude of the 
induced field is proportional to the value of the 
earth’s total magnetic intensity, H, H(Tr) 
designates the maximum transverse field at the 
detector due to an equivalent transverse soft 
iron bar. H(TL) is the maximum longitudinal 
field at the detector due to the same transverse 
bar. Thus, there are nine components of the 
induced field at the detector. Fortunately, as 
far as the effect on a total-intensity magnetic 
detector is concerned, TL produces the same 
kind of indication as LT ; TV produces the 


same kind of indication as VT ; and the same 
relationship is true for LV and VL. Further- 
more, during rolls LL is zero; and the indica- 
tions for VV and TT are of the same kind, but 
one is the negative of the other. During pitches 
TT is zero, and indications from the VV and 
LL components are of the same kind, one being 
the negative of the other. Therefore, it is neces- 
sary to compensate only the differences VV — 
TT and VV — LL. As a result, there are five 
components of the induced field to be considered 
when noise indications from the detector are 
being analyzed. 

The three parts of the magnetic field due to 
perm and the five parts due to the induced mag- 
netism of the aircraft must be compensated 
before maneuver noise from both perm and 
induced magnetic fields disappears at all dip 
angles. 

Permanent and Induced Fields — 
Compensation^-^ 

To compensate permanent fields, one pro- 
cedure consists of computing the proper values 
of the L, T, and V components from the indica- 
tions obtained during test maneuvers and in- 
stalling L, T, and V magnets to cancel these 
fields. This computation necessarily requires 
the measurement of the angles through which 
the aircraft is made to roll and pitch. Since it 
is not ordinarily convenient with this method 
to change the compensation in flight, several 
flights are usually needed to obtain the best 
compensation. More satisfactory results can 
be obtained and a considerable saving of flight 
time effected if an adjustable perm compensa- 
tor is mounted near the head. This compensator 
consists of three electromagnets with cores of 
permanent magnet steel. It is located 4 to 7 
feet from the detector and is oriented to give 
L, T, and V fields at the head. The magnetic 
moment of the cores can be altered in flight by 
passing a controllable magnetizing current 
through the proper coil and then removing the 
current, leaving the core with a controllable 
remanent magnetic moment (see Figure 10). 

Another method, which may be carried out 
on the ground without flight tests and is often 
satisfactory, is to locate^^* those parts of the 
airplane contributing to the permanent field 


CONFIDENTIAL 


88 


INSTALLATIONS OF MAD IN AIRCRAFT 




Figure 13. Magnetic field map for B-18. Hori- 
zontal components at wing-tip level. Measure- 
ments made with landing wheels down. 


and then deperm them. The deperming may be 
done by surrounding the part with a coil carry- 
ing direct current which is reversed at least 
a dozen times while its magnitude is gradually 
decreased to zero. Figure 11 illustrates such 
an operation. Alternating-current deperming 
proved inadequate due to eddy currents. To 
measure the magnitude of the magnetic fields 
on the ground, a stationary magnetometer 
(“perm detector”) is placed at the proposed 
position for the head ; and the airplane is 
hauled away from the magnetometer (Figure 
12). The field is measured on the four cardinal 
headings. The results should indicate the order 
of magnitude of the permanent and of the in- 
duced fields. Figures 13 and 14 show sample 
cases. If these measurements are carefully car- 
ried out, in a very quiet location, it is also pos- 
sible to determine the magnitude of some of 
the elements needed for the compensation of 
the aircraft.^-'i® 

There are two methods which may be used 
in neutralizing the elements of the induced 
field. The first method is the location of strips 
of Permalloy^" in the vicinity of the detector 
(see Figure 15). In the second method three 
coils furnish the L, T, and V fields, being fed 
from amplified indications of three saturated- 
core magnetometers fastened rigidly to the air- 
plane. This second method provides compensa- 
tion which is adjustable in flight, and it has 
been used to measure induced fields in new in- 
stallations. Its use is not recommended in Serv- 


CONFIDENTIAL 


COMPENSATION OF MAGNETIC FIELDS 


89 


ic.e aircraft unless it is found impossible to 
achieve satisfactory compensation with Perm- 
alloy strips. 

The location for the Permalloy strips is de- 
termined by the position of the equivalent mem- 
ber of the airplane. For example, in Figure 16, 
let the bar A represent the aerol strut as the 



Figure 14. Magnetic field map for Grumman 
NX1604. Horizontal components 5 feet above 
hangar floor. Landing wheels down. 


airplane is heading west. The magnetic inten- 
sity at the head 0 due to this strut consists of 
components TT and TL. The component TT can 
be neutralized by a horizontal Permalloy strip 
B with its center in the LV plane at the proper 
distance from the head O. In practice, a con- 
venient location for the compensating strip is 
aft of the head either inside the streamlined 
housing or fastened to the surface of the wing. 
The compensation of the TL component is not 
so convenient but may be effected either by the 
TL strips C or by the LT strips D. In the case 
of a wing-tip installation it is necessary to 
fasten the strips on an outrigger external to 
the streamlined housing. When strips are used 
in pairs like DD and CC, compensation of ten 
to one can be secured if the distance from the 


center of the strips to the center of the head is 
10 inches. If an 8.5-inch diameter housing is 
used, the outriggers extend about 6 inches out- 
ward from the housing. Such outriggers have 



-j 


Figure 15. Permalloy strips mounted on fins on 
streamlined housing. 

been successfully flown on the tail cones of 
Mark IV B-3-equipped PBY airplanes for the 
compensation of the LT field due to the control 
cables. 



Figure 16. Location of compensating strips. 


Eddy-Current Fields 

The eddy-current field^^-^ differs from the 
permanent and induced fields in that it is de- 
pendent on the time rate of change of the 


CONFIDENTIAL 


90 


INSTALLATIONS OF MAD IN AIRCRAFT 


orientation of the aircraft with respect to the 
earth’s field. It is caused by eddy currents flow- 
ing in the conducting skin and structural mem- 
bers of the aircraft. Slow maneuvers will pro- 
duce indications from the induced field, but the 
effect of the eddy-current field will be very 
small ; on the other hand, the eddy-current field 
may be enhanced by a rapid maneuver such as 
a fast roll or abrupt wingup. The indication 



caused by the induced field depends only on the 
heading and the amplitude of the maneuver, 
while that caused by the eddy-current field de- 
pends also on the speed of the maneuver. 

An analysis of eddy-current field shows that 
there are nine components. Again a double-let- 
tered nomenclature is adopted, consistent with 
the manner in which the eddy-current fields are 
produced and detected. These nine components 



Figure 18. Wing-tip installation in a PBY-5. 

arise from the changes in the three components 
of the earth’s field. A change of one of the com- 
ponents, for example, may give rise to a 
secondary field at the detector having X, Y, and 
Z components. This gives rise to the components 
tt, tl, and tv. Similarly, a change in will pro- 
duce components It, ll, and Iv; and a change in 
H, will give rise to the components vt, vl, and 
vv. 

At the outset it was found that eight of the 
nine components need to be compensated sep- 
arately. The components requiring compensa- 
tion may be {vv — tt) , {vv — ll ) , tl, It, vl, Iv, tv, 
and vt. Although this appears to be a more 
complicated situation than that of the perma- 


nent and induced fields, in practice the eddy- 
current components are more readily identifia- 
ble. Furthermore, from the point of view of 
MAD requirements, only the components of the 
eddy-current field created by a roll or a roll-like 
maneuver are important, since only that type of 
maneuver has sufficient angular velocities to 
excite troublesome eddy-current indications. 

Compensation of eddy-current fields has been 
accomplished by two methods. The nonelectronic 
method makes use of copper rings. An elec- 
tronic eddy-current compensator has also been 
built. For simple eddy-current fields the copper 
rings are preferable because of simplicity and 
uniform operation. The method is limited prin- 
cipally by the number of components which can 
be supplied without the introduction of addi- 
tional unwanted components. The electronic 


FI K1 SI 



compensator does not have this limitation but 
may be objected to because of its complexity 
and the additional weight involved. 


Compensation Flight Procedure 

In selecting an area for compensation 
flights,-- -® the geology of the region should be 


CONFIDENTIAL 


COMPENSATION OF MAGNETIC FIELDS 


91 


considered since areas must be found where the 
magnetic gradients are small or uniform. When 
prospecting for a favorable location, the change 
of total magnetic intensity per mile should be 
noted on the navigation chart with the heading. 
Large magnetic gradients of geological origin 
are likely to exiist where crystalline igneous 
rocks are outcropping or are buried at shallow 



Figure 20. Adjustable perm compensator, TS-7/ 
ASQ. 


depths. Where sufficient area cannot be found 
which is free from such rocks, flights may be 
made over deep water, or over shallow water 
at an altitude of 10,000 or 12,000 feet. Near 
Mitchel Field, New York, a quiet region was 
found centering at latitude 40° 19' N, longitude 
73°00' W. If many aircraft are to be compen- 
sated from a given base, it is well worth pros- 
pecting for a quiet region because it is then 
unnecessary to fly at high altitudes in order to 
get satisfactory records. 

The maneuvers used on compensation flights 
are rolls, pitches, wingups, and full turns. It is 
important that the pilot execute these maneu- 
vers as uniformly as possible. When special 
equipment for the measurement of the ampli- 
tude of the maneuvers is not available, ampli- 
tude is measured by means of the flight instru- 
ments on the pilot’s instrument panel. Whenever 
possible, the same pilot should fly the airplane 
until the compensation is completed, for it is 
then easier to compare the results from one 
flight to another. 


An average compensation flight requires from 
50 to 90 minutes depending on whether or not 
there are adjustable compensators on board. 
This does not include the time required to gain 
altitude, reach the starting point, and return to 
base. Three or four flights should be sufficient 
to compensate a new installation. One flight 
should suffice for the compensation of an addi- 
tional installation in the same type of aircraft. 

If the installation has been compensated by 
means of 15° rolls and pitches, it is well to check 
the compensation by violent maneuvers such as 



From X detector 



Figure 21. General electronic compensator for 
induced magnetism. 


45° wingups. Small adjustments of the com- 
pensation can then be made. 

Since the object of compensation is to reduce 
noise during tactical maneuvers, the final tests 
should consist of the most violent maneuvers 
that may be expected during the execution of 
a tactical problem. For these tests the recorder 
is connected to the regular ASQ amplifier, and 
the recorder tape is run at the speed of 6 inches 


CONFIDENTIAL 


92 


INSTALLATIONS OF MAD IN AIRCRAFT 


per minute. The clover-leaf executed at a 40° 
bank angle has been adopted as the ideal test 
because during this maneuver the aircraft goes 
into and out of a steep bank on four headings 
90° apart. One clover-leaf is executed with left 
270° turns and one with right 270° turns. The 
clover-leaf is started on a cardinal heading, 
and a straight run of about 10 seconds should 
be made following each 270° turn. For his rec- 
ord, the operator is informed by the pilot or 
copilot the instant the airplane is thrown into 


sequence of operations for the identification of 
the various magnetic terms to be compensated 
and for the installation of the proper compen- 
sation equipment. These procedures presuppose 
that no information concerning the components 
is available and that it is not possible to make 
any assumptions regarding the components. The 
use of this procedure as outlined in the chart 
will always result in a complete and satisfac- 
tory compensation of an MAD installation. 
When an actual installation is attempted, how- 



a turn, the heading at that instant, and the 
times at which the aircraft is on a cardinal 
heading. For a clover-leaf to the left, the se- 
quence is as follows: north, west, south, east; 
east, north, west, south ; south, east, north, 
west; west, south, east, north. It is sometimes 
useful to drop a float light on the water to 
insure that both right and left clover-leafs are 
flown over the same spot. 

An indication of the complexity of the prob- 
lem in the general case is given by Table 1, 
which is a diagrammatic representation of the 


ever, it is soon apparent that some of the com- 
ponents are zero or are sufficiently small to 
make certain steps in the chart unnecessary. If 
the eddy currents are not of sufficient magni- 
tude to be disturbing, they add no difficulty 
until low noise level is reached. Continuous ex- 
perience with a given type of aircraft often 
provides a great deal of useful information on 
the components to be expected in the installa- 
tion under consideration. Even when it is not 
possible actually to measure the moments of the 
ferromagnetic parts of the airplane, reasonable 


CONFIDENTIAL 


COMPENSATION OF MAGNETIC FIELDS 


93 


estimates may sometimes be made of the rela- 
* tive strength and direction of the field which 
might be expected from each part. 

Procedures as applied to two actual installa- 
tions in aircraft are described below. In no case 
were ground measurements available and there- 
fore the steps as followed correspond to the 
"‘flight measurement only” side of Table 1. 

PBY Tail-Cone Installation 

Analysis. Eddy currents are not present in 
a tail-cone installation in a PBY since the head 



Figure 23. Amplifier AM-36/ASQ for eddy- 
current compensator. 


is far removed from any large metallic sheets 
(see Figure 17). All nerm components may be 
present. T is probably small since the control 
cables to the elevators are the only transverse 
members near the head. L may be large from 
the control cables, and V may be large from the 
control cables to rudder and vertical sprocket 
chain of rudder control. The most probable 
source of induced field is LL from the control 
cables. Therefore, a program is built around the 
compensation of LL, T, L, and V. 

Procedure. It was found that the simplified 


assumptions in regard to this installation were 
justified. The procedure was as follows. 

1. T was compensated on north and south 
rolls by adjusting T until the fundamental in- 
dication was at a minimum. 

2. L was compensated by adjusting L on east 
and west pitches until the indication was at a 
minimum. 

3. On east and west rolls, V was adjusted 
until the indication was at a minimum. 

4. Finally, by pitching on north and south 
and measuring the indications, the required 
LL compensation was computed and added in 
the form of Permalloy strips on outriggers. 

PBY Wing-Tip Installation 

Analysis. Eddy currents in a wing-tip in- 
stallation in this airplane are no doubt mainly 
due to extensive wing surfaces and they are 
probably predominantly vertical (see Figure 
18). Because of the symmetry in the plane of 
the wings, no terms of the type of VT, VL, TV, 
LV, and V are expected. Large values of TL, 
TT, and LL are to be expected from the prox- 
imity of the wing float cross frame. Bomb racks 
and engines may contribute LL and VV, re- 
spectively. 

Procedure. 1. The pilot installation had 
fixed the position of the detector along the lead- 
ing edge to be feet inboard of the wing tip. 
The detector was experimentally placed 6 inches 
forward of the leading edge. The eddy currents 
were far too large to allow effective compensa- 
tion. The detector was moved to 28 inches for- 
ward of the leading edge, at which position 
eddy currents were found to cause indications 
of 14-gamma amplitude for the standard roll. 
The eddy-current indication was different in 
magnitude on the E and W headings, indicating 
the presence of a transverse component of the 
eddy-current vector. This component is prob- 
ably due to the rib structures forming closed 
loops in vertical-longitudinal planes. Therefore, 
electronic eddy-current compensation was used 
in this installation. An approximate correc- 
tion was applied by tilting the eddy-current 
output coil in the proper direction to help cor- 
rect for the transverse component. The total 
reduction of eddy-current noise was at least ten 
to one. 


CONFIDENTIAL 


94 


INSTALLATIONS OF MAD IN AIRCRAFT 


Table 1. 

USING GROUND AND 
FLIGHT MEASUREMENTS 


Outline of compensation procedure. 


USING FLIGHT 
MEASUREMENTS ONLY 


Ground measurements give 
TT 
LL 

rv 

LV 

TL 

LT 

Ground measurements do not give 

(a) Separation of the components in the terms 
T + VT sin </) 

L + VL sin (f) 

V + UF sin ct> 

(b) Eddy-current components 


IF EDDY-CURRENT 
COMPENSATOR IS AVAILABLE 


IF PERIVI COMPENSATOR 

IS AVAILABLE 

Perform actual compensation of eddy- 
current components, reducing noise to 
pure static indications. 


Determine the eddy-current compo- 
nents by reducing static indications to 
zero, using T, L, and V. 

Provide compensation. 



All eddy currents have been 





eliminated. 





Check flight, using right and left clover-leaf maneuvers, 

CONFIDENTIAL 



COMPENSATION OF MAGNETIC FIELDS 


95 


2. (TL + LT) was evaluated by rolling on 
N and S headings and making NR — SR. The 
residual was due to T. (TL + LT) was com- 
pensated. 

3. T was adjusted on N and S rolls until 
NR = SR = 0. 

4. L was adjusted on E and W pitches until 
EP=WP = 0. 

5. The indication on the E and W rolls was 
measured in order to evaluate TT. This com- 
pensation was installed, and indications on N 
and S pitches were measured for the evalua- 
tion of LL. 

When the aircraft had been compensated for 
T, L, (TL -f LT), and TT, but not for LL, the 


and this amount of compensation applied to the 
rest of the aircraft. The values proved to be 
correct in all cases and the same amount of 
eddy-current compensation was also required 
for all the aircraft. The permanent magnetic 
field was due to the welded and magnafluxed 
members of the cross frame and hence was 
completely random from aircraft to aircraft. 
The values were as follows. 


(TL + LT) 
TT 
T 
L 

LL 

The average 


45 gammas 
34 gammas 
—150 to +150 gammas 
—200 to +200 gammas 
45 gammas (not provided) 
noise level for a clover-leaf 



Figure 24. Circuit schematic of AM-36/ASQ eddy-current compensator. 


full circle maneuver was flown. The turn noise 
was nearly pure second harmonic which is 
unique to LL when (TV + VT) r= 0. This 
proved that the assumptions regarding the un- 
importance of VV and V were correct. However, 
because of certain limitations of expediency, 
LL compensation was not installed. 

Squadron Results. One airplane of a squad- 
ron of 15 was used for the detailed preliminary 
study as described above. The values of T and 
(TL + LT) were determined from this airplane 


maneuver was about 5 gammas maximum ex- 
cursion. It was due principally to the lack of LL 
compensation. However, the maneuver noise 
was of somewhat continuous character and not 
easily confused with true indications. When LL 
compensation was later provided, the noise level 
was reduced to 2.5 gammas. 

Service Compensation 

When an aircraft with its MAD installation 
is ready for service, it will have been compen- 


CONFIDENTIAL 


96 


INSTALLATIONS OF MAD IN AIRCRAFT 




sated for eddy currents and induced and per- 
manent magnetic fields. It has been found that 
the induced magnetic compensation will be un- 


months of active service a squadron of PBY-5’s 
showed negligible changes. On the other hand, 
a carrier-based TBF after some service has 


Figure 25. L pad and coils. 


OUTPUT COIL 


Figure 26. Eddy-current compensator input coil 
installed in a TBF wing. 

changed with service life. As yet, there is no 
evidence that the eddy-current compensation 
will require any change, but it is possible that 
it may. The perm in the aircraft is expected 
to change with length of service, though neither 
drastically nor often. For example, after two 


been known to show a marked deviation from 
original values. 

Thus, it is expected that periodically the air- 
craft will have to be recompensated for perm 
and examined for evidence of eddy-current 
change. The procedure for such an examination 
and adjustment of values is quite simple. The 
adjustable perm compensator is the only addi- 
tional equipment necessary. Without changing 
the magnetization of any of the coils, a record 
of pitches and rolls on the cardinal headings is 
first taken. This alone will give the operator 
some notion of the state of magnetic unbalance. 

The examination of the aircraft for eddy 
currents is done on the basis of change of am- 
plitude with change of frequency. T is adjusted 
until minimum noise is obtained on east head- 
ing, with a slow roll having an amplitude of 
15° and a period of about 12 seconds. The roll 
frequency is then doubled, the amplitude re- 
maining constant. If the indications for the fast 
roll are more than 50 per cent greater than 
those for the slow roll, there is positive evidence 
of need for adjustment of the eddy-current 
compensation. If an adjustable eddy-current 


CONFIDENTIAL 


COMPENSATION OF MAGNETIC FIELDS 


97 


compensator is part of the installation, its gain 
is changed until the indication on the fast roll 
is less than 150 per cent of the indication on 
the slow roll. 

Inasmuch as the operator will probably have 
no record of the previous magnetizing currents, 
he should next reduce to zero the moments of 
the perm magnets. The following steps will de- 

OUTPUT COILS MIXER INPUT COILS 


z z 



From X pickup coil and amp 



Figure 27. Schematic connections for most gen- 
eral case of eddy-current compensation. 


fine the entire perm compensation procedure. 

1. Pitch on east and west headings, adjusting 
L until EP == —WP. 

2. Roll on north and south headings, adjust- 
ing T until NR = —SR. 

3. Check the pitches on east and west heading 
for cross feed of T into L. It may be necessary 
to readjust L a small amount. 

4. Check the north and south headings, trim- 
ming T to the desired value. Roll on east and 
west headings adjusting V for minimum noise. 

5. The final check should be made by perform- 
ing the tactical clover-leaf, right and left. 


^ Compensation Equipment 

Table 2 is a summary of the various methods 
of compensation discussed above. The pieces of 
electrical equipment mentioned will now be de- 
scribed. 


Table 2. Summary of methods of compensation. 


Type of field 
to be 

compensated 

Active 

compensation 

Passive 

compensation 

IVrmanent 

Adjustable perm 
compensator and 
variable field electro- 
magnets. (Deperm 
all members pos- 
sible.) 

Proper placement of 
permanent magnets 
of the correct mo- 
ment determined by 
calculation. 

Induced 

Electronic induced 
compensating ampli- 
fier, with connected 
magnetometers and 
output coils. (This 
unit used experi- 
mentally only.) 

Strips of Permalloy 
positioned so as to 
cancel unwanted 
fields. 

Eddy current 

Electronic eddy-cur- 
rent amplifier, pick- 
up, and output coils. 

Copper rings or disks 
of the proper cross 
section, positioned 
properly to cancel 
out unwanted fields. 


The Adjustable Perm Compensator 

The adjustable perm compensator consists of 
three electromagnets with steel cores of high 




Figure 28. The a-c perm detector. 


retentivity maintaining residual moments up to 
4,000 cgs units. The electromagnets are 
mounted permanently in the airplane in such 
positions as to give three components at the 


CONFIDENTIAL 


98 


INSTALLATIONS OF MAD IN AIRCRAFT 


detector, one parallel to each of the three axes 
of the airplane, transverse, longitudinal, and 
vertical. There should be leads from the elec- 
tromagnets to the junction box of the MAD 
installation with connections for the operation 
of the TS-7/ASQ unit. This unit (see circuit 



Figure 29. Schematic circuit of the a-c perm 
detector. 


and photograph in Figures 19 and 20) operates 
on the 24-volt supply to the filament circuits of 
the MAD units and consists essentially of two 
potentiometers for coarse and fine control of the 
current in the electromagnets, and a current 
meter. A current-reversing switch makes it 
possible to reverse the polarity of the compen- 
sating magnets. 

The actual adjustment of the moments during 
flight can follow a rather straightforward pro- 
cedure. Since the signal is a direct indication of 
the needed compensating field, which in turn 
depends upon the moment of the magnet, a 


given disturbing field can be compensated by 
giving the electromagnets three or four values 
of current, and determining from a graph of 
current against signal the proper value of the 
current. It can be seen that this method of ad- 
justment depends upon no previous knowledge 
either of the disturbing fields or of the polarity 
of the compensating fields, but only upon a few 
readily determined points on a current versus 
signal graph. 

Electronic Compensating System 
FOR Induced Fields 

In this system, magnetometer detectors are 
installed rigidly in the plane with their axes 
parallel to the transverse and longitudinal 
plane axes. The signals resulting from the in- 
duced fields are amplified and combined as 
shown in Figure 21. The outputs are sent to 

r 



Figure 30. The d-c magnetometer element. 

coils attached to the plane so as to produce 
current whose magnetic fields will oppose and 
cancel the undesired fields. The circuit diagram 
of one of the amplifiers is shown in Figure 22. 
Although this system did not receive extensive 
tests, it was found possible in some trials to 


CONFIDENTIAL 


STD 2 STRIP DET 


COMPENSATION OF MAGNETIC FIELDS 


99 



CONFIDENTIAL 



100 


INSTALLATIONS OF MAD IN AIRCRAFT 


reduce the signals due to induced fields by a 
factor of 20 to 40. 

Eddy-Current Compensator'^*’ 

If a metal wing of an airplane moves through 
a magnetic field in such a manner that the total 


- 4 



Figure 32. Experimental setup for measuring 
eddy-current effects from a PBY wing. 


magnetic flux through the wing changes, then 
an electromotive force will be developed. This 
will cause eddy currents to flow in the wing and 
they will be proportional to the conductance of 
the metal. Also, the eddy-current loops will be 



Figure 33. Setup for field measurements with 
the three-component gradiometer. 


proportional to the wing area and will produce 
a magnetic field at right angles to it. To over- 
come this source of spurious indications the 
eddy-current amplifier, AM-36/ASQ, has been 
developed. It is shown in Figure 23. 

The AM-36 unit is a three-stage band-pass 
amplifier employing degenerative feedback. The 


input to the amplifier is the voltage picked up 
by a coil with a large number of turns and of 
large cross-section area. This coil is placed in 
the airplane in such a position that the radial 
plane of the coil is parallel to the eddy-current 
loop. The AM-36 amplifies the input voltage and 
provides a means for reversing its phase. The 
output of the amplifier is connected to the com- 
pensating coil which is usually placed about 1.5 
feet from the ASQ detector. When properly 
adjusted the current in this coil produces a mag- 
netic field which is equal and of opposite phase 
to the field produced by the eddy currents at the 
detector. Figure 24 is a schematic circuit dia- 
gram. 

The operating adjustments of this amplifier 
are readily made. The gain-controlling resistors, 
R19 and R20, are not installed at the time of 
manufacture but are selected by the person who 



Figure 34. Inside view of induction magnetom- 
eter. 


adjusts the unit. An L pad, shown in Figure 25, 
is inserted in place of the resistors by means of 
the jack connections, Jl, on the panel. As the 
airplane is maneuvered to produce eddy cur- 
rents, the gain of the AM-36 is adjusted by 
adjusting the L pad. When the correct gain has 
been determined the L pad is removed and the 
resistors, R19 and R20, corresponding to the 
two arms of the pad are inserted. Once these 
resistors are installed, the unit should require 
no further attention. Figure 26 shows a pickup 
coil installed in a TBF wing. 

In the most general case three input coils, 
three output coils, three amplifiers, and a mixer 
would be required — connected as shown in Fig- 
ure 27. However, it is evident that certain input 
and output coils are not required if the eddy- 


CONFIDENTIAL 


COMPENSATION OF MAGNETIC FIELDS 


lOI 


current field is simpler than the general case. 
For leading-edge or wing-tip installations, it 
has been found that the only evident eddy-cur- 
rent components are {vv — tt ) , tv, and vt. These 
three components may be obtained readily by 
using only one channel and tilting the input and 
output coils to obtain the cross terms.^^ 

In addition to the above three devices for ac- 
tive compensation in flight, various other pieces 



Figure 35. Pitch and roll indicator. 

of auxiliary compensation test equipment were 
developed. 

The A-C Perm Detector 

This device, a low-sensitivity magnetometer, 
was designed to serve as a detector in the de- 
perming of various struts and ferromagnetic 
members on aircraft. It is capable of measuring 
large fields without overloading, as it has nega- 
tive feedback in the magnetometer element 
drive circuit. The magnetometer element is of 
the conventional two-strip type encased in a 
bakelized linen tube and connected to the de- 


tector-amplifier by means of a flexible cable 
(Figures 28 and 29). This instrument will 
measure fields up to dz 12,500 gammas. 

The D-C Magnetometer^^ 

This test instrument was designed to fill the 
general requirements for the taking and record- 
ing of magnetic field strength measurements on 
the ground. Such measurements are required for 
landing gear struts, control cables, screws, rods, 
and other parts ; the required instrument must 
be stable and sensitive over a range from less 
than 1 gamma to hundreds of gammas. This 
instrument became the basic measuring device 
for making magnetic field measurements for in- 
stallations. It consists of a magnetometer con- 
nected to a d-c amplifier having a self-contained 
voltage-regulated power supply powered by a 
6-volt storage battery. It uses a double-strip 
magnetometer element with either a self-con- 
tained microammeter, an Esterline-Angus re- 
corder, or both as a means for reading and 
recording signals from magnetic fields. The 
detector element (Figure 30) is so mounted 



Figure 36. Towed bird with parallelogram bail. 


that three field components, mutually perpen- 
dicular to each other, can be taken by moving 
the element about its two (vertical and horizon- 
tal) mounting axes. The rough bias for neu- 


CONFIDENTIAL 



102 


INSTALLATIONS OF MAD IN AIRCRAFT 


tralizing the effects of the earth’s field is ob- 
tained by rotating a small magnet within the 
mounting block, while finer adjustments are 
obtained by varying the bias current within the 
amplifier. The circuit is shown in Figure 31. 

A three-component unit was also made up, 
consisting of three conventional magnetometer 
elements mounted mutually perpendicular. 
Their outputs were connected to separate ampli- 
fier channels and recording meters, thus allow- 
ing measurements of three components of field 
strength to be taken simultaneously. Typical 
of the sort of special investigations which could 
be undertaken with these magnetometers is the 
thick-iving study. (Figure 32.) 



Figure 37. Winch for towed bird installation in 
TBF airplane. 


The port outboard section of a PBY wing 
with trailing edge, retractable pontoon, and 
X-frame removed was mounted in a cradle. By 
means of a motor drive the wing could be moved 
to simulate pitches of the aircraft at a fre- 
quency of 0.2 c. The measurements were taken 
for a north heading of the aircraft. A d-c 
magnetometer was positioned at regular inter- 
vals along the center of rotation of the cradle. 


and field strength data taken for each position. 
Contour maps of the magnetic field strength 
were then plotted. The contours were found to 
agree with those calculated for a plain rectan- 
gular conducting sheet which is thicker at one 
edge than at the other. Additional data were 
taken with a flat aluminum sheet substituted 
for the wing. 

The Three-Component Gradiometer 

This instrument‘d was designed for the pur- 
pose of taking three-component magnetic field 
measurements simultaneously in the presence of 
noise from remote sources. The electronic cir- 
cuit of its three channels is essentially that of 
the three-component d-c magnetometer. The 
main difference is in the design of the detector 
elements. The two strips of the magnetometer 
element are separated by a distance of 50 feet 
or more and are connected as a gradiometer. 
In practice, one detector (the signal detector) 
is placed near to the field under measurement. 
The other (the reference detector) is placed at 
some distance, and the noise that affects both 
detectors alike will cancel. This instrument is 
most useful when magnetic field data are re- 
quired in locations where excessive magnetic 
disturbances from sources such as electric rail- 
road lines are present. The entire unit, includ- 
ing power supply, heads, and recorders, is 
shown in Figure 33. 

Low Sensitivity Induction Magnetometer 

This instrument^® was designed for use as a 
magnetic detector requiring no external con- 
nections other than a 3-volt dry battery. It con- 
sists of a standard d-c 1-0-1 milliammeter with 
its field magnet removed and replaced by a 
Permalloy dipole antenna. (Figure 34.) The 
dry battery is connected to the terminals of 
the moving coil which provides a fixed field. 
A current of approximately 80 ma passing 
through this winding produces a sensitivity of 
about ± 15,000 gammas full scale. In operation, 
the earth’s field is balanced out by means of a 
small rotatable magnet within the case, and the 
sensitivity may be adjusted by changing the 
constant field. This instrument also has possi- 

c Another gradiometer, devised by the Naval Ordnance 
Laboratory, is described in reference 35. 


CONFIDENTIAL 



THE TOWED BIRD 


103 


bilities for use as a pitch and roll indicator and 
as an induction-type d-c ammeter. 

Pitch and Roll Indicator 

This instrument was designed for use dur- 
ing compensation flights to facilitate the cor- 
relation of maneuver noise with the pitching 
and rolling maneuvers of the airplane. The in- 
dicator used in conjunction with this instru- 
ment can be either a microammeter (Figure 
35) or an Esterline-Angus tape recorder, the 
latter being useful when an analysis on the 
ground of maneuver noise and motions of the 
aircraft is necessary. 

This device is essentially a low-sensitivity 
magnetometer incorporating d-c negative feed- 
back as a means of stabilizing the detector ele- 
ment to keep it from overloading. The detector 
consists of two double-strip elements placed 
mutually perpendicular in a horizontal plane 
and so placed in the aircraft as to give indica- 
tions of the angular motions of the airplane 
with respect to the vector of the earth’s field as 
the plane flies on cardinal headings. The switch 
on the front panel is marked to denote pitches 
and rolls on the cardinal headings. 

Compensation Trainer 

A trainer was designed for the purpose of 
instructing personnel in compensation tech- 
niques. This device made possible the simulation 
of actual ferromagnetic and eddy-current fields 
in all types of Service aircraft. A problem could 
be set up by the instructor, solved by the stu- 
dent, and the results noted. The device was used 
jointly by the research staff and the training 
department of AIL for working out compensa- 
tion problems. 

The next sections take up the other method 
of eliminating the effects of magnetic noise 
from the aircraft. 


6.2 the towed BIRDI 

It is probable that if a noise level of less than 
2 gammas is needed during violent maneuver 
of the airplane, the head should be towed be- 

^ Some towed bird experiments were also carried out 
by the Naval Ordnance Laboratory.3"-39 


hind the plane in the manner shown in Figure 
8 of Chapter 1. And in general it is considered 
that the low noise level during straight and 
level flight with this system might increase the 
range of detection in service by as much as a 
factor of 1.5 compared to the compensated in- 
ternal installations. 

In early experiments,^® the streamline hous- 
ing or bird was designed to accommodate a 

f , , ■ ■ 



Figure 38. Behavior of towed bird during a roll. 

head-motor assembly of the general type used 
in MAD Mark IV equipment and was formed of 
an air-drying plastic material laminated with 
jute cloth. A tail structure comprising a cylin- 
drical fin of approximately the same diameter 
as the bird and spaced therefrom by four struts 
was provided to improve the aerodynamic sta- 
bility of the unit. This bird was suspended on 
a cable having 14 conductors and a phosphor 
bronze strain core. This cable was accommo- 
dated in the aircraft on a target-towing winch, 
and arrangements were made for flying the 
bird at various cable lengths. 

Two methods of attachment of the cable to 
the bird were investigated. In one of these the 
cable was connected directly to a fitting on the 
top of the plastic shell above the longitudinal 
center of gravity of the bird, while in the other 


CONFIDENTIAL 


104 


INSTALLATIONS OF MAD IN AIRCRAFT 


a bail structure was utilized which supported 
the bird at the center of gravity and permitted 
relative motion between the bird and the cable 
with 2 degrees of freedom. Initial experiments 
comparing these two types of attachment did 
not show any significant difference as far as 
performance was concerned, although with both 
it was found that the bird had much less sta- 
bility than the towing aircraft and that the 
servo system of the detection equipment was 
not capable of following relatively fast motions 
of the bird transmitted thereto by the cable. In 
addition, it was found that when relatively 
short cable lengths were used variations in the 
separation between the aircraft and the bird 
during maneuvers or rough air caused noise. 
Such noise was presumably due to changes in 
the effect of the magnetic field of the aircraft 
on the detection equipment and was eliminated 
in later experiments through the use of cable 
lengths of approximately 200 feet. 

In an effort to improve towed bird perform- 
ance, various means were investigated for 
damping the motion of a bail-suspended bird. 
In one of the damping systems rubber was used 
to provide a restoring force, while in another a 
hydraulic damper in which oil was carried from 
one chamber to another through an adjustable 
orifice was used. A third type of damper in- 
volved the use of mercury in a coiled tube 
which was mounted inside the bird. 

At about the same time, a flight test was made 
to determine the feasibility of mounting the 
bird on a 12-foot strut which could be lowered 
while the aircraft was in flight to provide a 
rigid support for the bird beneath the aircraft. 
While no difficulty was encountered in raising 
or lowering the strut, persistent vibrations at 
amplitudes and frequencies such that detector 
operation was impractical were encountered. 
This, plus the fact that support problems would 
obviously become more difficult as the strut was 
extended to practical lengths, caused abandon- 
ment of this approach in favor of the cable 
method of suspension. 

The development of the type AN/ASQ-1 
equipment with the relatively small DT- 
1/ASQ-l head and a more efficient servo system 
added impetus to the towed bird investiga- 
tion.^i’^- A streamline wooden housing of the 


type used for wing-tip installations was fitted 
with a tail structure of aluminum and an im- 
proved bail for attachment to the towing cable. 
This equipment is shown in Figure 36. The 
aluminum tail structure, which was later re- 
placed by one of plastic, was cylindrical in form 
and had a diameter which was the same as the 
largest diameter of the bird. This structure was 
supported by four longitudinal fins, two of 
which were vertical and two of which were 
horizontal. The bail structure was designed to 
isolate the bird from forces which would other- 
wise be transmitted to it by the connecting 
cable. This so-called parallelogram bail provided 
2 degrees of freedom permitting the bird to 
pitch and roll. 

The bail structure included two nonmagnetic 
ball bearings which were mounted in Dural 
plates on either side of the housing at the longi- 
tudinal center of gravity, which was artificially 
located approximately one-third of the distance 
from the nose to the tail by means of segmental 
lead weights mounted inside the housing. Two 
short rods extending from the bearings to the 
outside of the housing provided a support axis 
normal to the longitudinal axis of the bird. 
Hollow arms, each equal in length to the diam- 
eter of the housing, were pivoted at the outer 
ends of the rods, and the upper ends of these 
arms pivotally connected to a third hollow arm 
which completed the parallelogram. The several 
hollow arms and rods accommodated the elec- 
trical connections from the towing cable to the 
head-motor assembly. This structure permitted 
motion of the bird in respect to the cable with 
2 degrees of freedom. Initially, the towing cable 
was connected to the bail by a standard Amphe- 
nol AN-type connector, rigidly connected to the 
upper bar of the parallelogram. This arrange- 
ment was soon replaced with the one shown in 
the illustration, in which the plug was pivoted 
to allow motion of the cable in respect to the 
upper bail arm about an axis parallel to the 
longitudinal axis of the bird, thereby prevent- 
ing oscillations of the cable from exerting any 
forces tending to cause the bird to roll. 

Initial experiments were carried out using a 
cable having 14 conductors and a phosphor 
bronze strain cable ; this was replaced for later 
experiments by a special cable having no strain 


CONFIDENTIAL 


THE TOWED BIRD 


105 



Figure 39. Mark IV B-2 MAD rack installation in K-type blimp. 


CONFIDENTIAL 



106 


INSTALLATIONS OF MAD IN AIRCRAFT 


cable and 12 solid conductors. This cable was 
accommodated on a target-sleeve towing reel 
(Figure 37) with the connections at the inner 
end of the cable brought out to a connector 
mounted on the reel. This equipment, together 
with the remaining units of an AN/ASQ equip- 
ment, was mounted in a type PBY-5A airplane 
for testing, the reel being so positioned that 
the bird could be flown from the tunnel hatch. 
After the bird had been lowered to the desired 
cable length, the reel was locked, and electrical 
connections were made between the AN/ASQ-1 
equipment and the connector mounted on the 
reel. 

A large number of test flights were made at 
Quonset Point, and simultaneous records were 
taken with bird-mounted and tail-cone-mounted 
equipments. In a comparison of these simulta- 
neous records, it was found that a somewhat 
lower average noise level for straight and level 
flight could be obtained with the towed bird 
than with the equipment mounted directly in 
the aircraft. During maneuvers, the bird fol- 
lowed the aircraft well if the maneuver was 
executed smoothly. (For example, see Figure 
38.) However, during very sudden maneuvers 
the system was less stable. 


6 3 mad service installations 

Between July of 1941 and July of 1944, over 
400 installations of MAD equipment were made. 
While many of these installations were actually 
made by the Services, most of them were de- 
signed or supervised by Laboratory personnel. 

Lighter-than-Air Installations 

While the early MAD experiments were made 
in Navy PBY airplanes, the first Service instal- 
lations were made in the blimps at the Lake- 
hurst Naval Air Station. The success of these 
early installations was such that MAD became 
standard equipment for all blimps in antisub- 
marine service. Figure 39 shows the standard 
Mark IV B-2 rack installation in the forward 
portion of the control car. Over 100 of these 
installations were made in K-type airships. 

In the fall of 1943, an experimental installa- 
tion of AN/ASQ-2C equipment was made on a 


K-type airship. More of these installations were 
made in the spring of 1944, and by the middle 
of 1945 more than 60 K-type airships had been 
so equipped. 

As it is possible to locate the magnetometer 
head at a considerable distance from the steel 
structure of the control car and engines, and 
as the maneuvers of an airship are considerably 
less violent than those of an airplane, it usually 
has not been found necessary to compensate 
LTA installations. 

Heavier-than-Air Installations — 

Mark IV B-2 

The early experimental tests were made with 
the magnetometer head mounted in the hull of 
a PBY-1 patrol bomber. While this type of 
installation was useful for experimental work, 
it was unsatisfactory for Service use as the 
head was too near personnel and material in 
the airplane. Later installations were made with 
the head mounted in the extreme rear of the 
hull. Where the dip angle is about 70° little 
trouble is encountered in satisfactorily com- 
pensating the permanent fields of the airplane. 
Tests made at San Diego and Key West indi- 
cated, however, that for lower dip angles such 
compensation would be difficult. 

In the spring of 1942, the Army initiated an 
extensive program of MAD installations in B-18 
airplanes in a tail cone. The appearance of this 
was such that it was quickly and aptly called 
a “stinger.” Under the general supervision 
of AIL, a total of approximately 100 installa- 
tions of this type were made. During August 
of 1942, an experimental installation was made 
in the tail of a B-25 medium bomber. Because 
of the presence of a large amount of steel fit- 
tings, the installation was unsatisfactory. In 
September of 1942, an experimental installa- 
tion was started on an Army B-34 bomber. A 
special Mark IV B-2 head was designed in order 
to make possible the use of a smaller tail cone, 
but no Service use was made of MAD in this 
airplane. Following the success of the B-18 
tail-cone installation, a similar mounting was 
designed for use of PBY’s. This proved very 
successful and placed the equipment in a posi- 
tion relatively free from disturbing magnetic 
fields, which made for easy and reliable com- 


CONFIDENTIAL 


MAD SERVICE INSTALLATIONS 


107 


pensation. Several experimental installations of 
this type were made at Quonset, and an entire 
squadron (VP-63) was so equipped at San 
Diego. 

Heavier-than-Air Installations — 
AN/ASQ-1, 1A,*2, 2A 

With the development of the lightweight, 
compact AN/ASQ-1 equipment, dual installa- 
tions in large airplanes became practical and 
single installations in small airplanes economi- 
cal from the weight standpoint. 

Fifty-seven of these installations had been 
made by July 1944. 


Field Engineering 

Because of the speed with which MAD equip- 
ment went into Service use and because it rep- 
resented a new type of equipment for which 
there was little background of experience, AIL 
had to furnish a considerable amount of field 
engineering assistance. Laboratory engineers 
were sent to many of the lighter-than-air bases 
and with most of the MAD-equipped squad- 
rons.'^^'^^ These engineers aided in the installa- 
tion and maintenance of equipment, helped train 
Service personnel, and brought back to the 
laboratory information needed for the design 
of new equipment. 


CONFIDENTIAL 


Chapter 7 

TRAINING DEVICES AND EXPERIMENTAL EQUIPMENT 


7 1 MAGNETIC ATTACK TRAINER 
General Description 

T he type 3 magnetic attack trainer [MAT- 
SI is intended for use in training blimp 
personnel in the tactical use of AN/ASQ and 
sono buoy equipment. It provides means for 
simulating at a reduced scale the tactical con- 


original magnetic attack trainer,^ which was 
built and permanently installed at the Airborne 
Instruments Laboratory during the winter and 
spring of 1943 and was used in the training of 
both lighter- and heavier-than-air personnel of 
the U. S. Navy. The improved trainer was con- 
structed for the lighter-than-air branch and 
was particularly designed for such use. 

It was required that the trainer be a com- 



Figure 1. Perspective drawing of MAT-3. 


ditions occurring in the use of the equipment, 
thereby permitting personnel to be trained 
without necessitating withdrawal from service 
of actual material. 

The MAT-3 is an improved model of the 


plete unit in and of itself which could, if neces- 
sary, be moved from place to place. Certain 
improvements leading to more realistic simula- 
tion of the tactical problem were also requested. 

The MAT-3, shown in Figure 1, includes a 


108 


CONFIDENTIAL 


MAGNETIC ATTACK TRAINER 


109 


scale model tactics area in which a model sub- 
marine and a model blimp may be maneuvered 
independently in response to separate sets of 
remote controls. The submarine model is pro- 
vided with means for generating a magnetic 
field scaled to that of an actual submarine and 
varying properly with changes in heading. Suit- 
able adjustments are provided so that sub- 
marines having various types of magnetization 
may be simulated for any desired magnetic dip 
angle. 

The blimp model is provided with simulated 
AN/ASQ equipment which is arranged to de- 
tect the magnetic field of the submarine model 
and to produce output indications simulating 
with a high degree of verisimilitude those ob- 
tained with the AN/ASQ equipment under cor- 
responding conditions. The speeds of the two 
models and the vertical distance between them 
(representing the altitude of the blimp plus the 
depth of the submarine) may be varied to dem- 
onstrate the effects of these factors on the 
operation of the AN/ASQ equipment. The ef- 
fects of wind on the operation of a blimp may 
also be simulated. The MAT-3 is arranged to 
simulate either the AN/ASQ-1 or AN/ASQ-2B 
installations as desired. 

Since in actual practice the blimp pilot can- 
not see the submarine, the tactics area in the 
MAT-3 is so positioned as to be out of sight of 
the pilot-trainee. Such information as to the 
position of the blimp and its course as may be 
available to the pilot of an actual blimp during 
a tactical period is made available to the pilot- 
trainee in the MAT-3 by means of an indicating 
system. This system includes a scale model of 
the tactics area which is mechanically linked 
to the blimp model drive and moved beneath a 
fixed observation point in accordance with the 
movements of the model blimp in the tactics 
area. The observation point, which represents 
the blimp, is located close to the surface of the 
scale model in order to maintain realism. Ac- 
cordingly, an optical system is provided by 
means of which the pilot-trainee is effectively 
positioned at the observation point. 

The float lights or flares used in conjunction 
with the AN/ASQ equipment are reproduced 
and appear on the scale model ocean of the 
pilot’s indicating system. Also provided are 


means for simulating the dropping of bombs 
from the blimp and for recording the results of 
bombing attacks. 

A second indicating system operates a record- 
ing table on which the paths of both the sub- 
marine and blimp models during a training 
exercise are permanently recorded for reference 
purposes. The locations of the two models at 
the instant when bombs or flares are dropped 
are also recorded. This indicating system forms 
part of the equipment provided for the use of 
an instructor. The instructor is also furnished 
with duplicates of the blimp controls and with 
controls for the submarine model. 

Certain of the control and indicating equip- 
ment of the MAT-3 is provided in duplicate so 
that an aviation radioman (ARM) and a pilot 
may be trained simultaneously, each perform- 
ing the duties which he will perform in actual 
practice. 



Figure 2. Tactics area, MAT-3. 


The sono buoy training equipment includes 
means for simulating submarine sounds and 
background noises as heard from buoys dropped 
at a number of positions in the tactics area. 
The signals from the listening positions may be 
monitored selectively at the pilot’s and ARM’s 
positions using headphones. An intercommuni- 
cation system connecting the instructor’s, pilot’s 
and ARM’s positions also utilizes the head- 
phones and the amplifiers associated therewith. 

The MAT-3 equipment is mounted on a struc- 
tural steel framework 10 feet 4 inches by 12 
feet by 9 feet 6 inches high, which is supported 
at the four lower corners. This structure con- 
sists of two decks, the upper of which is occu- 
pied by a tactics area 8 by 10 feet reproducing. 


CONFIDENTIAL 


110 


TRAINING DEVICES AND EXPERIMENTAL EQUIPMENT 


at a scale of 300 feet to 1 inch, an area approxi- 
mately 4.8 nautical miles north and south by 6 
nautical miles east and west. The submarine 
and blimp models and their associated trans- 
lating mechanisms are accommodated on this 
deck and are shown in Figure 2. The lower 
deck is laid out as shown in Figure 3 and ac- 
commodates the electronic equipment mounted 
in relay racks; the pilot’s, instructor’s, and 


^ Blimp and Submarine Translation 
Systems 

The blimp and submarine models are mounted 
for movement in the tactics area on suspensions 
similar to those used in bridge-type cranes. The 
submarine model is mounted on a carriage 
arranged for movement back and forth along a 
beam which is itself arranged for movement 



ARM’s control positions; the pilot’s indicating 
system ; and the recorder table. 

The control and drive systems and the elec- 
tronic equipment of the entire trainer are shown 
in operating relationship in Figure 4, pictorial 
schematic of MAT-3. 


over the tactics area. The beam provides for 
movements of the model in the east and west 
direction while the carriage provides for travel 
in the north and south direction. 

The suspension for the blimp model is simi- 
lar in all respects to that of the submarine 


CONFIDENTIAL 


MAGNETIC ATTACK TRAINER 


111 


PILOT’S 

POSITION 

D-ATt OF^ 
TUft.W 


CLOCKO'^t^n 


MAGNETIC 

OJMPASS^ 

GYtO. 

compass'^ 

AID.6PEEI; 
bLIMPf 
WOOL 


RATE OF/ 
TUIEN 

bLlMPfl 
RUDDE 
CONT 
BLIMP I 
5Pt£D| 

CONT 



^ T-v-L macnlti4ation 
5UPPLY 

(z) 4) 

O C. ^ 

ml 


GEAlL-bOX ELECTRONIC CIRCUIT 
LLGLMD 


Figure 4. Pictorial schematic of MAT-3. 


CONFIDENTIAL 






















112 


TRAINING DEVICES AND EXPERIMENTAL EQUIPMENT 


model and is mounted immediately above the 
latter in such fashion that the two models may 
move independently to all positions in the tac- 
tics area without interference. Motion is trans- 
mitted to the respective beams and carriages of 
the blimp and submarine translation systems 
by means of four cable systems which pass 
around four drive drums located on the lower 
deck of the MAT-3. These four cable systems 
are independent and those for the two beam 
movements are so arranged that the beams are 


may be appropriately adjusted to establish the 
required rate of turn. This is accomplished by 
means of rotatable transformers, the shafts of 
which are driven through reduction gearing by 
a motor controlled by the rate-of-turn control. 
One of these rotatable transformers is arranged 
to produce a voltage varying with the sine of 
the angle through which its shaft is rotated, 
while the other is arranged to produce a voltage 
proportional to the cosine of the same angle. 
Since the motor speed is proportional to the 



restrained from yawing and binding in their 
guides as they move over the tactics area. 

Each of the four cable-system drive drums is 
rotated by means of a d-c motor. Since the steer- 
ing controls of a blimp or submarine establish 
a rate of turn, it is necessary that mechanism 
be provided to obtain, from the rate of turn so 
established, information in accordance with 
which the rectilinear velocities of the beam and 
the carriage of the associated translation system 


desired rate of turn, the shaft rotation of the 
rotatable transformer may be made a direct 
measure of the heading angle. The control sig- 
nal obtained from each of these rotatable trans- 
formers is thus an a-c voltage, the amplitude of 
which varies in accordance with the sine or 
cosine, respectively, of the heading angle and 
the phase of which reverses at zero. A special 
motor control system is provided to operate the 
d-c translation-system drive motors in response 


CONFIDENTIAL 


MAGNETIC ATTACK TRAINER 


113 


to a-c control signals, this system being de- 
signed also to provide substantially constant 
torque at all motor speeds between zero and 
a maximum speed and to produce a motor 
speed which is a linear function of the control 
voltage unless the motor is actually stalled. 

The motor control systems^ each comprise 
four units in addition to the controlled d-c 
motor. These units are a phase-sensitive de- 
modulator, a “constanC’-current power supply, 
a motor control amplifier, and a permanent- 
magnet generator. Briefly, the a-c control sig- 
nal is demodulated to obtain a d-c voltage which 
varies in amplitude and polarity with the am- 
plitude and phase of the control signal. This 
d-c signal is used to control a d-c motor with 
separately excited armature and field windings, 
the armature being supplied from a substan- 
tially constant current source. The d-c control 
signal is power amplified and supplies the field 
current, variations in which cause correspond- 
ing variations in the speed and direction of 
rotation of the motor. The permanent-magnet 
generator is coupled directly to the shaft of the 
motor and supplies a feedback voltage to the 
motor control amplifier such that variations in 
speed of the motor due to changing loads are 
overcome. A complete motor control system of 
this type is shown in Figure 5. 

In the operation of a typical motor control 
system embodying these units, the application 
of an a-c control signal to the input of the 
phase-sensitive demodulator causes the produc- 
tion of a d-c potential at the input of the motor 
control amplifier. This results in a large in- 
crease in the field current of the motor which, 
assuming that the armature is excited with 
"‘constant’' current, causes the motor to start, 
the direction of rotation depending on the phase 
of the a-c motor control signal. The motor 
drives the permanent-magnet generator, the 
output of which is very nearly linear with 
speed. The polarity of the generator output 
voltage is such as to oppose the signal at the 
input of the motor control amplifier. This 
causes a decrease in the motor speed, which in 
turn reduces the voltage fed back to the con- 
trol amplifier from the generator. Accordingly, 
the system reaches an equilibrium speed for a 
given signal voltage. The motor control ampli- 


fier, being responsive only to the difference in 
voltage between the control and feedback sig- 
nals, causes large changes in field current 
whenever the motor speed changes by a few 
rpm whether the motor is operating at high or 
low speeds. Thus the motor delivers torque 
even at very low speeds since any force tending 
to reduce the shaft speed causes a large increase 
in field voltage tending to accelerate the motor 
until the equilibrium speed determined by the 
signal voltage is re-established. 

This motor control system is used for all 
motor drives in the MAT-3. In a typical in- 
stallation shown in Figure 6, two armature 



Figure 6. Motor control system racks, MAT. 


power supply units, a chassis housing two 
phase-sensitive demodulators, and two motor 
control amplifiers are mounted in a single relay 
rack, together with a single motor drive unit. 
A single rack thus accommodates a complete 
motor control system plus all the units of a sec- 
ond system with the exception of the motor and 
the generator. 

As mentioned above, each of the four cable 
systems of the blimp and submarine drive sys- 


CONFIDENTIAL 


114 


TRAINING DEVICES AND EXPERIMENTAL EQUIPMENT 


terns is driven by means of a d-c motor con- 
trolled by one of the motor control systems just 
described. In the blimp translation drive sys- 
tems provision is made to permit overrunning 
of the drive after the beam and carriage have 
reached the limits of their travel. However, this 
drive system permits the pilot-trainee to per- 
form maneuvers beyond the limits of the tactics 
area, motion of the blimp model in the area 
always starting at the angle and position de- 
termined by the maneuver performed in the 
overrun area. 

Steering Control Systems 

The submarine steering control system is 
operated from the instructor’s position as shown 
schematically in the pictorial schematic of the 
MAT-3, Figure 4. The control wheel, which 
establishes a rate of turn, turns a center-tapped 
variable autotransformer providing an a-c con- 
trol signal, the phase of which varies with the 
direction of turn and the amplitude of which is 
dependent upon the rate of turn. This control 
signal is used to control a d-c motor through a 
motor control system of the type described 
above. The speed of the submarine along its 
path is determined by the voltage applied to 
the single phase windings of the rotatable trans- 
formers, this voltage being controlled by means 
of an autotransformer operated by a control 
wheel at the instructor’s control position. Since 
the turning radius of a submarine remains sub- 
stantially constant for all speeds, it is neces- 
sary to increase the speed of the submarine 
rate-of-turn motor drive as the submarine speed 
is increased. This is accomplished by applying 
a portion of the output voltage of the submarine 
speed control autotransformer to the submarine 
steering control autotransformer. 

The blimp steering control system is similar 
to the submarine steering control system and, 
as shown in the pictorial schematic. Figure 4, 
may be operated from either the pilot’s or the 
instructor’s positions. A switch is provided at 
the instructor’s position for shifting the control 
from a center-tapped variable autotransformer 
at that position to an identical autotransformer 
at the pilot’s position. In either case the auto- 
transformer provides an a-c control signal 
which determines the operation of the motor 


control system. The speed of the blimp along its 
path is controlled by varying the voltage ap- 
plied through a variable autotransformer to 
the single phase windings of the rotatable 
transformers mentioned above. Provision is 
made for simulating the effects on the course 
of the blimp due to winds having various 
velocities. Such winds are simulated by apply- 
ing additional control voltages to' one or both 
of the blimp translation system motor drive 
units. The proper voltages for this purpose are 
obtained by means of two potentiometers, one 
for north-south wind components and one for 
east-west wind components, located at the in- 
structor’s control position and connected to the 
output of a regulated 75-volt d-c power supply. 
These potentiometers provide a range of wind 
velocity adjustment for each cardinal direc- 
tion extending from 0 to 40 knots. Winds from 
intercardinal directions are simulated through 
the use of both control voltages. 

For convenience, all adjustments in the ver- 
tical separation between the blimp and sub- 
marine are effected by means of an elevator 
associated with the submarine model. A dif- 
ferential control system responsive to blimp 
altitude and submarine depth controls is pro- 
vided to govern the operation of the elevator. 
The blimp altitude control system includes a cen- 
ter-tapped variable autotransformer by means 
of which an a-c signal of proper phase and 
amplitude is applied to the input of a motor 
control system. The submarine dive-control 
wheel actuates a second motor drive system 
which drives a second selsyn generator through 
a gear box. At the upper limit of the range the 
stop mechanism operates a “surface” switch 
which doubles the speed of the submarine model. 
The rotation of the differential selsyn on the 
submarine model is proportional to the algebraic 
sum of the rotations of the two selsyn genera- 
tors included respectively in the blimp and 
submarine altitude and dive control mecha- 
nisms. Accordingly, the total separation be- 
tween the two models is appropriately varied 
by the single elevator on the submarine model 
whether changes in the separation between the 
two are due to changes in the altitude of the 
blimp, changes in the depth of the submarine, 
or both. 


CONFIDENTIAL 


MAGNETIC ATTACK TRAINER 


115 


^ Blimp, Submarine, and Detector 
Models 

The submarine model shown in Figure 7 is 
mounted on the carriage of the submarine 
translation system. The dimensions of this 
model are scaled to those of a typical submarine 
at a scale of 300 feet to 1 inch and means are 
provided for simulating the magnetic field of 
the prototype. The model is mounted on a ver- 
tical shaft rotatably supported on the sub- 
marine carriage and driven by the submarine 
heading selsyn receiver through a train of spur 
gears. A circular rack is cut in the shaft and a 


field of the submarine to be simulated. The sys- 
tem is equivalent to that used in the model 
signal studies described in Chapter 4. 

The blimp model is mounted on the carriage 
of the blimp translation system and includes a 
pair of pickup coils mounted to simulate the 
port and starboard detectors of an AN/ASQ-2B 
installation. Provision is made also for simulat- 
ing the operation of the ASQ orientation sys- 
tems. The pickup coils are mounted for rotation 
about horizontal axes supported by a pair of 
vertical shafts. These shafts are rotatably 
mounted on a column extending vertically from 
the blimp carriage and itself mounted for 



Figure 7. Blimp and submarine models. 


second train of gears driven by the elevator 
differential selsyn receiver is arranged to raise 
and lower the shaft in respect to the carriage. 
The required connections to the three magnetic 
field generating coils on the submarine model 
are made through slip rings mounted on the 
shaft. Also mounted on the submarine model 
carriage is a target model which forms a part 
of the simulated bombing system. 

The magnetic field of a submarine is simu- 
lated in the MAT-3 by means of an a-c field, 
the amplitude of which is made to vary in 
accordance with the amplitude variations of the 
d-c field of an actual submarine and the phase 
of which is determined by the polarity of the 


rotation in respect to the carriage. Back gear- 
ing and flexible linkage between the column 
drive and the two pickup coil shafts maintain 
a constant space orientation of the horizontal 
coil-supporting axes irrespective of rotations 
of the vertical column. The two pickup coils are 
thus maintained in parallel vertical planes at 
all times, and their orientations in these planes 
may be adjusted manually to simulate opera- 
tion at locations of different dip angles. A 
plastic cover encloses the pickup coils and pro- 
tects them from injury without in any way 
impairing their operation. Orientation of the 
blimp model in accordance with the heading 
determined by the pilot’s steering control is 


CONFIDENTIAL 



116 


TRAINING DEVICES AND EXPERIMENTAL EQUIPMENT 


effected by means of a selsyn receiver mounted 
on the blimp carriage and driving the column 
through a set of spur gears. The control signal 
for the selsyn receiver is obtained from a 
selsyn transmitter driven through appropriate 
gear reduction by the blimp rate-of-turn motor 
drive. 

Mechanism to be described below is also 
mounted on the blimp carriage for use in con- 
nection with the simulated bombing system. 

As pointed out above, a-c excitation is used 
for simulation of the magnetic field of the 
submarine, and the AN/ASQ detectors are 
simulated by means of simple pickup coils. 
The output from each of these coils is a 400- 
cycle voltage, the phase and amplitude of which 
vary as the coil is carried through the a-c field 
of the submarine model. The signals from the 
two pickup coils are fed to separate channels, 
each comprising a signal amplifier and de- 
modulator and a replica of the a-c amplifier and 
band-pass filter stages of AN/ASQ-1, in the 
manner of Chapter 4. 

The AN/ASQ click test is simulated in the 
signal amplifier and demodulator unit by im- 
posing a 400-cycle signal in phase quadrature 
with the reference signal upon the input of the 
unit. The click test signal is obtained from the 
400-cycle supply and its phase is shifted by 
means of an RC circuit. A switch is closed to 
impose the click test signal simultaneously 
upon the inputs of both channels of the unit. 

Output connections directly from the plates 
of the second amplifier are provided for use 
with the CM-2/ASQ unit and provision is made 
for the introduction of background noise of the 
type generally encountered in the AN/ASQ 
equipment to the input circuit of the amplifier. 
Background noise is produced by means of 
photoelectric cam systems, one of which is pro- 
vided for each of the port and starboard de- 
tection channels. The noise generator unit 
which includes equipment for both channels is 
shown in Figure 8. Light from a pair of exciter 
lamps falls respectively through Y-shaped slits 
upon a pair of photoelectric cells which are 
connected across the output of a regulated 
power supply. Four different optical cams, 
driven at slightly different speeds, are so posi- 
tioned in relation to the two slit systems that 


in the case of each photoelectric cell three cams 
cooperate to regulate the amount of light fall- 
ing thereon. The output voltage from each of 
the photoelectric cells is applied to two cathode 
follower stages. The background noise level is 



Figure 8. Bottom view of noise generator. 

adjusted by varying the current in the exciter 
lamps. 

A standard CM-2/ASQ unit is included in 
the MAT-3 for use in tactical training. The 
input signals for this unit are obtained from 
the two detection channels as described above 
and the output from the unit may be utilized to 
operate the simulated flare and bomb circuits. 
Dual wiring is installed so that the CM-2 may 
be used in either the instructor’s or the ARM’s 
position. 


Instruments and Indicators 

The pilot-trainee is provided with controls 
and instruments simulating those of an actual 
blimp, it being noted, however, that in the case 
of the MAT-3 the pilot-trainee operates the 
rudder control while air speed and the eleva- 
tors are controlled by a second person (ordi- 
narily the instructor) . The pilot’s control posi- 
tion, which is shown in Figure 9, includes an 
adjustable seat, an instrument panel, a switch 
box, and a rudder wheel. 

The rudder control wheel, which is spring 
loaded through a heart-shaped cam to simulate 
the “feel” of a blimp rudder control, operates 
the center-tapped variable autotransformer 
which controls the blimp rate-of-turn motor 
drive. The pilot’s instrument panel shown in 
Figure 9 includes a rate-of-turn meter, a clock. 


CONFIDENTIAL 


MAGNETIC ATTACK TRAINER 


117 



Figure 9. Pilot’s control position. 
CONFIDENTIAL 



118 


TRAINING DEVICES AND EXPERIMENTAL EQUIPMENT 


magnetic compass, a gyrocompass, an air speed 
meter, an AN/ASQ sum meter, an AN/ASQ 
left-right meter, an altimeter, and a rate-of- 
climb meter. 

The switch box includes bomb and flare re- 
lease switches, switches for controlling the 
CM-2/ASQ, and pilot lights showing the con- 
ditions existing in certain of the control cir- 
cuits. 

An indicating system, shown in Figure 10, 
is provided to give the pilot-trainee only that 


upper and lower carriage which are arranged 
to travel in mutually perpendicular directions.- 
The lower of these carriages is mechanically 
linked to the blimp east-west motor drive shaft, 
while the upper carriage is mechanically linked 
to the blimp north-south motor drive shaft. 

In order to obtain a high degree of realism, 
the model tactics area is made of cyanite glass 
the surface of which closely resembles the 
ocean surface in appearance. This glass is sup- 
ported by means of a Plexiglas plate in the 



Figure 10. Pilot’s optical table. 


information as to his position over the tactics 
area which he would have available in actual 
practice. This system takes the form of a scale 
model of the tactics area, scaled at 1,200 feet 
to 1 inch, which is movable in respect to a 
fixed index representing the position of the 
blimp. This model is mounted on a rectangular- 
coordinate translation system including an 


lower surface of which are recessed concentric 
cold cathode tubes which provide blue-green 
illumination and serve to light the ocean sur- 
face from beneath. A cyclorama of sand-blasted 
Plexiglas surrounds the model ocean and is 
back-lighted by means of conventional fluores- 
cent lamps to simulate the sky. 

The pilot-trainee is effectively positioned at 


CONFIDENTIAL 


MAGNETIC ATTACK TRAINER 


II9 


the location of the index representing the blimp 
by means of an optical system^ the eyepiece of 
which is located in the pilot’s control position 
immediately above the instrument panel as 
shown in Figure 9. The optical system com- 
prises a periscope, the lower mirror of which 
is mounted on the index representing the blimp 
model, an erecting prism, and a unity power 
telescope. A binocular eyepiece is provided at 
the pilot’s position. The lower periscope mirror, 
the erecting prism, and a pair of spot lights 
which provide additional illumination in the 
direction of vision are mounted on an optical 
turret supported over the model ocean, while 
the remainder of the optical system is mounted 
between a pair of I-beams extending horizon- 
tally across the compartment in which the model 
ocean is located. The lower periscope mirror 
is rotated by means of a selsyn receiver so that 
the pilot’s vision is always in the direction in 
which the blimp is headed. This selsyn receiver 
is of the differential variety, and one set of 
its windings is excited from the heading selsyn 
in the blimp rate-of-turn mechanism. The erect- 
ing prism (Dove type) is also driven by this 
differential selsyn through appropriate reduc- 
tion gearing which causes its angular velocity 
to be one-half that of the lower mirror. 

The second set of windings of the differential 
selsyn which drives the optical turret is excited 
by a selsyn generator, driven through gearing 
by means of a hand crank on the pilot’s instru- 
ment panel. This control, known as the “look 
around,” enables the pilot to scan the horizon 
irrespective of the optical system heading de- 
termined by the blimp rate-of-turn drive. 

The instructor’s position includes controls 
for both the blimp and submarine models, ap- 
propriate blimp and submarine instruments, 
controls for the field component simulators and 
the sono buoy simulating equipment. The re- 
cording table is also located at this position. The 
following controls and instruments provided at 
the pilot’s position are duplicated at the in- 
structor’s position: the rate-of-turn meter, the 
magnetic compass, the air speed meter, the al- 
timeter, the rate-of-climb meter, and the blimp 
rudder control. The blimp speed and altitude 
are also controlled from the instructor’s posi- 
tion. 


A recording table, shown in Figure 11, is pro- 
vided at the instructor’s position to indicate 
the relative paths of the blimp and submarine 
models in the tactics area and to provide a 
permanent written record of these paths. This 
recording table comprises essentially a small 
model (scaled 1,200 feet to the inch) of the 
blimp-submarine tactics area on the upper 
deck of the MAT-3. Translation systems for 
indexes simulating the blimp and submarine 
models are driven by cable systems from the 
blimp-submarine gear box. A sheet of paper, 
mounted between the recording table carriages 
representing the blimp and submarine models, 
is used as the recording surface, and pens 
mounted on the two carriages of the recording 
table translation systems make continuous 
traces of the paths of the two models. The pen 
on the lower carriage is required to write up- 
side down on the lower surface of the paper 
and operates through capillary action. The 
recording paper is translucent, and both traces 
may be seen simultaneously from above. The 
recording table also incorporates means for re- 
cording the positions of the two models at the 
instants when flares are dropped or bombing 
attacks are made. 


^ ^ ^ Bomb and Flare Model Systems 

Means are provided in the MAT-3 for simu- 
lating the marking flares or floatlights used 
during tactical operations. For this purpose, 
mechanism is mounted on the optical turret for 
depositing a small drop of mercury on the model 
ocean whenever a flare release is tripped. In 
addition, the instructor’s recording table is so 
arranged that a mark may be made on the trace 
representing the path of each of the models 
whenever a flare is released. This mechanism 
includes means for translating the paper frame 
of the recording table through a small circle, 
thus causing the recording pens to form a cir- 
cular trace at the positions which they occupy 
at the time the flare is released. The paper 
frame is mounted on a torsion rod suspension, 
and an eccentric cam is arranged to rotate the 
suspension through a small circle. A heavy 
clock spring drives the cam through a one- 


CONFIDENTIAL 


120 


TRAINING DEVICES AND EXPERIMENTAL EQUIPMENT 



Figure 11. Instructor’s position and recording table. 

CONFIDENTIAL 


MAGNETIC ATTACK TRAINER 


121 


revolution clutch which permits one marking 
operation each time the flare release is tripped. 
A small electric motor rewinds the spring as 
required, this motor being stalled when the 
spring is fully wound. 

The MAT-3 also includes means whereby a 
bombing attack may be simulated and the re- 
sults of such an attack recorded. The bombs are 
simulated by means of high-tension sparks 
which may leap between an array mounted on 
the blimp model and target wires mounted on 
the submarine model. Referring to Figure 7, 
the bomb array is rotatably mounted on the 
blimp model carriage and comprises a series 
of parallel needles spaced to represent one 
stick of the bomb pattern to be simulated. The 
shaft on which the array is mounted is geared 
to the blimp-model-supporting column and turns 
therewith so that the array is always at right 
angles to the longitudinal axis of the blimp 
model. 

The target model comprises a pair of target 
wires, one of which is mounted slightly above 
the other and represents the vulnerable area 
of the submarine, while the other represents 
the area surrounding the submarine in which 
a near hit may be scored. These wires are 
mounted on a rotatable support which is driven 
through gearing from the submarine heading 
selsyn, and the longitudinal axis of the target 
array is maintained parallel to the fore-and-aft 
axis of the submarine model at all times. 

Means are provided for simulating the drop- 
ping of three sticks of bombs at chosen inter- 
vals. The high-tension sparks, simulating the 
bombs, are produced by means of an induction 
coil through which a capacitor is discharged 
by means of a thyratron whenever a firing 
relay is closed by an electromechanical timing 
system. 

The timing system includes an intervalometer 
which trips the firing relay three times at 
chosen intervals whenever a bomb release but- 
ton is depressed. The intervalometer is pro- 
vided with three mechanical cams mounted for 
relative rotation on concentric shafts which 
may then be locked together and driven as a 
unit by means of an electric motor. A latch 
engaging a slot in the first cam stalls the 
electric motor and prevents rotation of the 


cams until removed. This latch is withdrawn 
by means of a release relay when the bomb re- 
lease switch is closed. This relay also closes a 
pair of contacts which actuate the flare simula- 
tor circuits described above ; in addition it 
closes a circuit to a switching relay which 
connects the hit and near-hit target wires to the 
first hit and first near-hit indicator channels of 
the bomb hit indicator to be described below. 
As the intervalometer shaft revolves, switches 
associated with the second and third cams are 
successively closed to send second and third 
pulses to the firing relay. Simultaneously, ad- 
ditional switching relays are closed to connect 
the target wire circuits to the second and third 
hit and near-hit inputs of the bomb hit indi- 
cator. The relative angular positions of the 
three cams may be varied by means of panel 
controls to vary the spacing between successive 
sticks of bombs. The first and last sticks may 
be separated by any time between 0 and 7 
seconds and the second stick may be made to 
fall at any time between the first and third 
sticks or simultaneously with either of them. 

The bomb hit indicator includes three hit 
indicator channels and three near-hit indicator 
channels to which the hit and near-hit target 
wires are respectively connected in proper 
order by means of the switching relays in the 
bomb release circuit. The six indicator channels 
are identical and each includes a thyratron and 
a pair of neon indicator lamps. One set of in- 
dicator lamps is located at the instructor’s 
position while a second set is mounted on the 
pilot’s instrument panel. If the relative posi- 
tions of the blimp and submarine models when 
the bomb release is tripped are such that a 
spark from the bomb array reaches a target 
wire, it is imposed through an RC delay circuit 
upon the grid of the thyratron in the proper 
indicator channel. The threshold of the thyra- 
trons is set by means of a reference voltage 
obtained from a regulated power supply in- 
cluded in the bomb indicator unit. A canceling 
relay is operated from a push button on the 
operator’s control panel to remove the plate 
voltage from the thyratrons, to extinguish 
thereby any indicator lamps after the score 
has been determined. 

The MAT-3 includes apparatus simulating 


CONFIDENTIAL 


122 


TRAINING DEVICES AND EXPERIMENTAL EQUIPMENT 


the expendable sono buoy detection system so 
that training in its use in conjunction with the 
AN/ASQ equipment may be carried on. This 
apparatus includes means for generating sub- 
marine sounds as heard in the sono buoy re- 
ceiver and also contains means for simulating 
the hiss background noise commonly heard 
along with the submarine sounds. Submarine 
sounds including motor noises and propeller 
threshing are simulated by means of a partially 
filled box of barley grains rotated through a 
gear train by a motor control unit controlled 
by the submarine speed control. The gear train 
and the box are mounted in a soundproof en- 
closure which also includes a microphone. The 
grinding of the gears and the sounds of the 
barley grains in the box provide realistic simu- 
lation of submarine sounds. 


'2 OTHER TRAINING ACTIVITIES 

The Airborne Instruments Laboratory found 
it necessary to conduct training courses® in the 
operation, maintenance, and tactical use of 
ASQ equipment. At first this training was done 
in a rather informal manner and was usually 
conducted in the field. In the summer of 1943 
a school was set up at Mineola to give special 
ASQ training to Service personnel. 

Hangar 7, Roosevelt Field, was partitioned 
to make available six rooms to the training de- 
partment. These consisted of an office, two lec- 
ture rooms, a room for trouble shooting and 
maintenance training, a projection room for 
showing motion pictures and other visual train- 
ing material, and a large room which was fur- 
ther divided by screens to provide laboratory 
space for maintenance and construction work 
as well as space for operator training. In addi- 
tion, the magnetic attack trainer was used in 
the training of pilots and operators. The Lab- 
oratory airplane was made available for flight 
training in operation and signal recognition. A 
sunken tanker off Barnegat Light was used 
as a target; on special occasions permission 
was obtained to fly over Ambrose Lightship.'^’ ® 

A section of the laboratory room was 
screened off to make room for the installation 
of eight AN/ASQ-1 sets complete with CP-2 


units. A “duck” or signal simulator and its 
auxiliary amplifiers, specially constructed to 
provide signals simulating those obtained with 
AN/ASQ-1 mounted in TBF, PBM, and PBY 
airplanes and in lighter-than-air ships, was 
controlled by the instructor. It could be used as 
either a single or dual installation. This ar- 
rangement made it possible for the instructor 
to furnish identical signals simultaneously to 
all students. 

In addition to MAT, the pantograph tactics 
trainer® was used. This is essentially a panto- 
graph mounted on a table divided in half with 
a shield so that a person seated on one side of 
the table is unable to see the position of the 
stylus on the other side. The instructor sits on 
one side to plot the course of the submarine. 
When the pilot moves his stylus to describe the 
path of the airplane flying AN/ASQ-1 tactics 
patterns, the stylus on the instructor’s side 
follows the same pattern, and when it passes 
over the position of the submarine a contact is 
reported by the instructor to the pilot. This 
trainer was used as a preliminary training de- 
vice. 

The compensation trainer mentioned in Chap- 
ter 6 consisted of a standard AN/ASQ-1 set 
together with a TS-7/ASQ perm coil com- 
pensating control box, a d-c amplifier, and a 
cradle allowing rotation about longitudinal and 
transverse axes to simulate roll and pitch. At 
the same time the cradle could be rotated about 
a vertical axis to give any heading. Problems 
in compensating permanent fields were pro- 
duced by placing permanent magnets at suitable 
positions on the cradle. Compensating magnets 
of the correct strength were adjusted by the 
student to cancel the fields thus produced. In- 
duced signals were produced by placing Permal- 
loy strips in suitable position on the cradle 
with appropriate compensation achieved by 
having the student place other strips in such 
positions as to cancel these original fields. 

Technician Training. This course was de- 
signed to cover a period of four or five weeks. 
It presupposes that the student has had about 
ten months of previous training. Where it was 
thought advisable elementary electricity was 
covered in review, but the actual contents of 
the lectures and the time spent depended to a 


CONFIDENTIAL 


SUGGESTED ALTERNATIVES FOR AN/ASQ COMPONENTS 


123 


great extent on the student's previous training 
and experience. Considerable latitude was al- 
lowed the student so that he could concentrate 
on those phases where he seemed to need the 
most help. All students were required to keep 
notebooks on laboratory work including de- 
tailed analyses of all troubles encountered in 
the trouble shooting course. 

Pilot Training. The pilot training course was 
designed to give pilots a general background 
of knowledge in antisubmarine activities and 
to give them specific and thorough training in 
the equipment procedures and tactics employed 
in the field of magnetic detection. It was planned 
to cover a period of about two weeks. 

Operator Training. This course was planned 
to cover a two-week training period for aircraft 
radiomen who were to be AN/ASQ-1 or AN/ 
ASQ-2 operators. It included a qualitative ex- 
planation of the principles involved, a very 
thorough training in operational procedures, 
handling of the equipment, and a general back- 
ground concerning auxiliary equipment such as 
sono buoy, radar, and various types of ordnance. 
During the last two days of this course the 
operators worked with the pilots on the mag- 
netic attack trainer. This offered a very close 
approach to actual operating conditions and 
put emphasis on teamwork and understanding. 

In addition to these courses regular flights 
in the laboratory airplane were scheduled for 
all pilots and aircraft radiomen at the Mineola 
Training School. 

At the San Diego School where personnel of 
complete squadrons were trained, the individual 
crews were given the opportunity of getting 
used to the particular aircraft they were to op- 
erate. To enable them to fly AN/ASQ-1 tactics, 
in full scale, dropping flares and bombs, a 
magnetic target was constructed. A piece of 
8-inch well casing 20 feet long, filled with ap- 
proximately 100 half-inch SAE 1020 mild steel 
rods, was mounted in a wooden frame which 
could be pivoted about its center. A coil of 
closely wound No. 12 wire on an aluminum 
sleeve was fitted over the pipe and connected 
to a gasoline-driven generator which supplied 
approximately 750 watts of power to the coil. 
This produced a magnetic moment of 1.3 X 
cgs. 


In addition to these training activities vari- 
ous members of AIL served from time to time 
as consultants to the Jam Handy Organization 
in the preparation of five strip films which 
were used by the Navy training program for 
LTA and HTA. These films covered the fol- 
lowing aspects. 

1. What is MAD? 

2. Preoperation check. 

3. How it works. 

4. Signal characteristics. 

5. Flight characteristics. 

Another visual training aid in the form of a 
16-mm sound-on-film movie entitled “MAD Sig- 
nal Recognition" was made by the Navy Photo- 
graphic Unit at Anacostia, D. C. Two members 
of the AIL scientific staff assisted as technical 
consultants during the preliminary production 
stage of this film. 

^ » SUGGESTED ALTERNATIVES FOR 
AN/ASQ COMPONENTS 

The following sections list a number of sug- 
gestions for alternatives to parts of the pro- 
duction MAD systems. Some of these were 
merely discussed, while others were tried out 
on a laboratory scale. 

7.3.1 Three Component Detector- 
Magnetometer 

From time to time the suggestion is made 
that a magnetometer head be designed employ- 
ing three mutually perpendicular magnetometer 
elements.^**’ The complete scheme involves the 
use of three mutually normal elements, a squar- 
ing circuit for the output signal of each ele- 
ment, and provision for adding the squared 
signals obtained. The obvious advantages of 
such a sequence of operations is the resulting 
simplicity and compactness of the magnetom- 
eter head due to the elimination of all orienta- 
tion equipment. 

However, certain precision requirements on 
the aforementioned sequence of operations make 
such a device difficult of realization. The four 
principal limitations will be considered sep- 
arately. The desired maximum error is assumed 
at about 0.1 gamma in a total field of 50,000 
gammas. 


CONFIDENTIAL 


124 


TRAINING DEVICES AND EXPERIMENTAL EQUIPMENT 


Limitation on Orientation of Axes. Take the when computed under these conditions turns 
axes X, Y, and Z in perfect orthogonality, out to be 7 minutes of arc. 

Ideally, the axes of the three elements would Alloivable Squaring Error. Take the equation 



Figure 12. Minor magnetic disturbance at Tucson, September 28, 1944. 


lie in coincidence with these three axes. Per- 
fectly linear detection and perfect squaring and 
summing will be assumed in this case. The 
maximum allowable disorientation of one axis 


in the form where p repre- 

sents an exponent of the x term slightly di- 
vergent from 2. Assume perfect orientation of 
the elements, exact squaring of the y and ^ 


CONFIDENTIAL 


SUGGESTED ALTERNATIVES FOR AN/ASQ COMPONENTS 


125 


components, linearity of detection in all ele- 
ments, and proper summing of the squared 
responses. The allowable error in squaring turns 
out to be of the order of 0.001 per cent. 

Permissible Linearity Error. Take the equa- 
tion S — ^/x- + y- 

As before, assume perfect orientation of the 
elements, exact squaring of all components, 
proper summing of the square responses, and 
precise square root extraction. Consider linear 
detection in y and and nonlinear detection in 
X. The allowable deviation from linearity may 
then be shown to be of the order of 0.0002 per 
cent. 

Limitation on Summing. Take the equation 
S = \/ gx“ -\- y- -f- Z“. 

Here also assumptions are made of perfect 
orientation of the elements, linear detection in 
all elements, perfect squaring of all components, 
proper summing of y~ and z~ but not x-, and 
precise square root extraction, g differs slightly 
from unity. 

Analysis of this equation shows that the sum 
should be correct to within 0.0004 per cent of 
any of the squared terms. 

The above considerations will begin to give 
an insight into the stringent demands on the 
components of a magnetometer designed along 
the lines indicated. 

' Wave-Train Magnetometer 

This was an experimental magnetometer,^^* 
and no research was carried beyond the pre- 
liminary breadboard stage. The field-sensitive 
output of the magnetometer bridge consists of 
oscillations at a frequency of the order of 10 
kc. These oscillations are modulated by the 
drive frequency (400 c) and its harmonics. 
The amount of fundamental drive frequency 
present in the modulation is proportional to the 
external field and changes phase at zero field, 
while the modulation is at twice the drive fre- 
quency. 

The wave trains are obtained by tuning the 
magnetometer coils with shunt capacity and 
tuning the output circuit to the same frequency. 

A demodulator and amplifier were constructed 
for use with this magnetometer, and test rec- 


ords taken. The records indicated satisfactory 
operation, but in view of the existence of suit- 
able magnetometers no further research was 
done. 


Feedback Detector 

The purpose of this project was to investigate 
the effect of a system of degenerative feedback 
on the performance of a peak-type detector and 
if possible to develop a simple conversion for 
the AN/ASQ equipment then in production. 

This arrangement exhibited fairly constant 
sensitivity over a wide range of unbalance, and 
signals originating in the equipment resulting 
from filament and plate voltage changes were 
practically nonexistent. Microphonic distur- 
bances were reduced somewhat and the re- 
quirement for accurate selection of components 
was eased. 

The frequency response was found to be 
about the same as for the AN/ASQ-1. It was 
found as before that the magnetometer bridge 
was the main source of noise. 


Carrier System for CM-1 

In order to eliminate the long time constants 
of the circuits used for interstage coupling in 
the CM-1 unit, a new system was developed. 
The signals from the right and left AN/ASQ-1 
units of a dual installation are used to modulate, 
by means of ring modulators, a 400-c carrier 
supplied from the oscillator of one of the units. 
The modulated carrier is then amplified by 
transformer-coupled amplifiers from which 
sum and difference signals are obtained. These 
signals when demodulated serve to operate 
flare and bomb circuits similar to those in the 
CM-1 unit. One of these units was built and 
bench-tested but never underwent a flight test. 
The system was found to be quite reliable. The 
modified unit was lighter in weight and re- 
quired fewer tubes than the one in use. Be- 
cause of the urgency of other work and the 
existence of a suitable comparator unit, no 
further research was done. 


CONFIDENTIAL 


126 


TRAINING DEVICES AND EXPERIMENTAL EQUIPMENT 


OTHER LABORATORY STUDIES 
AND EQUIPMENT 

Two other special studies carried out by AIL 
should be mentioned. These dealt with the re- 



sponse characteristics of various RC filters for 
signals of the MAD type and with the intensity 


of fluctuations of the earth's field in the MAD 
signal frequency range. The results of the 
former are presented in the references listed 
in the bibliography.^® -^ The investigation of 
fluctuations of the earth's field-^’ 22 
considerable detail, both on Long Island and 
at the Magnetic Observatory of the U. S. Coast 
and Geodetic Survey at Tucson, Arizona. Most 


Table 1. Summary of MAD production and testing 
done at Airborne Instruments Laboratory, 1942-1944. 


Production totals 


MAD Mark IV B-2 equipments 

(less magnetometer heads) 86 

MAD Mark IV B-2 head assemblies 150 

MAD Mark IV B-2 motor assemblies 123 

MAD Mark IV B-3 equipments 

(modified Mark IV B-2) 25 

AN/ASQ-1 (Mark VI) equipments 170 

HG-7 magnetometer head units 23 

DT-l/ASQ-1 units 66 

DT-lA/ASQ-1 units 4 

DT-3/ASQ-1A units 150 

DT-3A/ASQ-1A units 51 

“U” units (AM-9/ASQ-1A prototype) 20 

AM-9/ASQ-1A units 200 

“0” and ‘‘0-1” units (CP-2/ASQ-1 prototype) 24 

CP-2/ASQ-1 units 51 

CM-l/ASQ-2 units 73 

CM-2/ASQ-2B units 39 

“X” units (AM-36/ASQ prototype) 17 

AM-9/ASQ units 7 

Signal simulator units (TS-160/ASQ-2 prototype) 6 
TS-160/ASQ-2 units 6 

“Q” units (T'S-7/ASQ prototype) 14 

Fluxmeter discriminator units CLU-53212 10 

CU-36/ASQ-2 units 16 

Equipments tested 

Mark IV B-2 476 

AN/ASQ-1 170 

CM-l/ASQ-2 72 

CM-2/ASQ-2B 39 

AM-9/ASQ-1A 200 

CP-2/ASQ-1 51 

DT-l/ASQ-1 89 

DT-3/ASQ-1 150 

DT-3/ASQ-1A 50 


of the charts showed little which could be 
identified as variations in the earth’s magnetic 
field at frequencies in the 0.1 -c to 1.0-c hand. 
Figure 12 shows the trace of a minor disturb- 
ance as recorded with a band-pass amplifier 
and the Esterline-Angus recording meter on 
September 28, 1944. Figure 13 shows a record 
taken during an electrical storm. Note that the 
maximum amplitude is less than 0.04 gamma. 


CONFIDENTIAL 




OTHER LABORATORY STUDIES AND EQUIPMENT 


127 


On a typically quiet day the amplitude was less 
than 0.002 gamma. 

Various other items of special equipment 
proved useful for MAD research. Among these 
were Helmholtz coils^^ and double-walled Perm- 
alloy cans^^ for producing small, magnetically 
quiet volumes arid standard coils designed to be 
used in place of permanent magnets^^ for cali- 
brating MAD equipment. A fairly elaborate 
signal simulator (labeled as TS-160/ASQ-2) 


was also built for production testing and ad- 
justment of the dual CM-1 and CM-2 units. 

In addition to the research, development, 
training, and field installation work described 
previously, AIL carried out considerable pro- 
duction and testing of Service MAD units. 
Table 1 summarizes the latter activities. It may 
be noted that the complete test for an 
AN/ASQ-1 equipment requires about 15 man- 
hours. 


CONFIDENTIAL 


Chapter 8 

USE OF MAD FOR LAND TARGETS 


Although ASQ equipment was developed 
l\. for the detection of submerged enemy sub- 
marines, its usefulness is not necessarily limited 
to this single objective. The equipment has been 




Figure 1, Tape record of signals obtained from 
passage over a convoy of 30 trucks. A. Altitude 
150 feet. B. Altitude 100 feet. 


investigate the feasibility of detection of such 
targets^’ - as industrial plants, ship yards, me- 
chanical field equipment, and fixed gun em- 
placements. This chapter describes the result 
of flights over such ferromagnetic objects at 
low altitudes as well as the use of AN/ASQ 
equipment as a navigational aid through the 
recognition of known anomalies associated with 
the terrain. 


« 1 DETECTION OF MECHANIZED 
FIELD EQUIPMENT 

The large masses of iron in mechanized field 
equipmenU-5 distort the earth’s magnetic field at 
a sufficiently great distance to be detectable 
from MAD-equipped aircraft. Although the 
magnetic effects from motorized equipment are 
small in magnitude, they are much more sharply 



used to aid in the search for submerged objects 
other than submarines. It is logical to consider 
the use of this equipment for the detection of 
other iron objects which are obscured from 
view by darkness, clouds, or camouflage. 

A number of test flights have been made to 


Figure 2. Record of signals from search of five 
areas. Altitude 100 feet. 

localized than those from ordinary terrain. To 
a great extent, the latter can be removed by 
electrical filters in the MAD apparatus, as 
modified for use in these flights. Early tests, 


128 


CONFIDENTIAL 



DETECTION OF MECHANIZED FIELD EQUIPMENT 


129 


which were made over a truck convoy, indicated 
that operation, at the rather necessarily high 
speed of the B-25 and at the low altitudes re- 
quired for satisfactory detection, resulted in 
faster signals than those for which the AM-1/ 
ASQ unit was designed. Accordingly, these sig- 
nals were amplified less than the slower ones of 
geologic and maneuver noise, and detection of 



Figure 3. Line of mechanized field equipment. 

Altitude 100 feet. Airspeed 135 mph. 

small targets with the standard AM-l/ASQ 
unit was found to be difficult. 

To secure the optimum signal-to-noise ratio, 
it was necessary to modify the pass band of 
the AM-l/ASQ unit by decreasing its low-fre- 
quency response. The required changes were 
accomplished by reducing the coupling capaci- 
tors in the last two stages of the AM-l/ASQ 
to 0.1, a switch being provided so that either the 
normal or the altered band might be used selec- 
tively. 


Even with the modified amplifier it was found 
necessary to fly at an altitude of less than 125 
feet in order to obtain useful signals from 
trucks and armored vehicles. Figure 1 shows 
the tape record of a series of passes made over 
a convoy of approximately 30 trucks spaced at 
30- to 70-yard intervals. In another test, passes 
were made over five areas identified as areas 



Figure 4. Terrain near Port Jefferson. Altitude 
100 feet. Airspeed 135 mph. 


A, B, C, D, and E, which were searched in 
simulation of an actual tactical situation. One 
of the areas contained a well-camouflaged tank 
battalion which was correctly identified as area 
C after passes had been made over all five. The 
tape records of Figure 2 were made during 
passes over the five areas and show clearly the 
basis on which the correct area was identified. 

To determine the reproducibility of the sig- 
nals from several representative pieces of 
mechanized field equipment, flights were made 


CONFIDENTIAL 



130 


USE OF MAD FOR LAND TARGETS 


repeatedly over units set up in a straight line. 
These units used were : 

1. 4 1 / 2 -inch howitzer MlAl 

2. 105-nim howitzer M3A1 



Figure 5. Battery of 16-inch guns. Altitude 1,025 
feet. Airspeed 135 mph. 


3. 155-mm gun Ml 

4. 40-mm Bofors gun AA, M2A1 

5. Half-track 

6. Tank destroyer 

7. 21 / 2 -ton truck 

8. 2 tank destroyers 

9. Bivouac 

The truck (item 7) was considerably out of 
line with the rest and was missed on all but 
one pass. Signals obtained for a representative 
pass over these objects are reproduced on Fig- 
ure 3. The circled numbers on the charts corre- 
spond to the number of the object as tabulated 
above. The airplane did not always fly directly 


over all the objects and as a result the signal 
amplitude for a particular piece of equipment 
does not always bear the expected relationship 
to the altitude. It may be noted that the mag- 
netic moment is likely to vary by as much as a 
factor of four between units of the same type. 

Despite their small amplitude, the signals 
from this field equipment stood out well above 
the noise level. This is due in part to the mag- 
netic homogeneity of the terrain used. 

Figure 4 is a record taken at an altitude of 
100 feet over fairly bad terrain just east of 
Port Jefferson, Long Island. The trace shows 
slow changes of large amplitude. A set of sharp 



Figure 6. Batteries of 6-inch guns and 16-inch 
guns. Altitude 400 feet. Airspeed 135 mph. 


signals, such as those on Figures 1 to 3, super- 
imposed on the traces of Figure 4 could usually 
be identified as originating from concentrated 
masses of iron. In this case the magnetic rocks 
are considerably below the surface. When the 


CONFIDENTIAL 



DETECTION OF COAST-ARTILLERY GUN BATTERIES 


131 


terrain consists of granite, basalt, and volcanic 
rocks on or near the surface, the effects may 
entirely mask the signals from mechanized 
equipment. 

The AN/ASQ-IA equipment can be used only 
to indicate when the searching aircraft is above 



Figure 7. Coastal fortifications. Altitude 230 
feet. Airspeed 135 mph. 


a target ; it cannot be used to guide the aircraft 
to a target. The principal difficulty in the use 
of the equipment for this purpose is found in 
the problem of briefing the navigator with suf- 
ficient accuracy to permit location of suspected 
areas on the first attempt. In addition, con- 
ventional navigation methods are difficult to 
apply with sufficient precision at the high speed 
and low altitude at which the operation must 
be carried out. 


« 2 DETECTION OF COAST-ARTILLERY 
GUN BATTERIES 

Flights were made over the fortifications of 
Fort Hancock, New Jersey, which consist of 
two 16-inch guns, two batteries of two 12-inch 
guns per battery, a battery of two 6-inch guns, 
and a battery of disappearing 12- and 14-inch 
guns. Surprisingly large signals and low noise 
levels were obtained, assuring the detection of 
the 16-inch guns from an altitude of 1,300 feet. 
Measurements were made both with the stand- 
ard detector and with the detector with less 



feet. 

low-frequency response. The former is better 
suited for altitudes greater than 200 feet. 

Figure 5 shows the signal obtained with the 
modified detector while flying at 1,025 feet over 
the 16-inch guns. At 1,325 feet an identifiable 
signal was also recorded with the standard de- 
tector. The 6-inch guns appear on the trace of 


CONFIDENTIAL 



132 


USE OF MAD FOR LAND TARGETS 


Figure 6. The run shown on Figure 7 was in- 
tended to portray what a hedge-hopping air- 
craft would find while flying over coastal 
fortifications. The flight path was not always 
directly over the targets. The objects causing 
the signals are labeled on the record. 

The magnetic moments of the guns were 



Figure 9. Philadelphia. Altitude 1,700 feet. 


estimated from extrapolation of the data from 
model experiments. They are: 

16-inch guns 3.4 X cgs each 

12-inch guns 3.0 X 10-^ cgs per battery 

of two guns 

6-inch guns 1.0 X 10^ cgs for two guns 
The airplane was also flown over a railroad 
gun and the moment was estimated to be 0.25 
X 10^ cgs. The battery of 12- and 14-inch dis- 
appearing guns gave a signal equivalent to a 
0.25 X 10^-cgs source. These last two values are 
questionable; the remaining magnetic moment 


calculations should be within a factor of two of 
the actual values. As was mentioned previously, 
there is little information available concerning 
the moments of steel structures such as these. 
However, it is to be expected that, as a result 
of being fired while parallel to the earth’s mag- 
netic field, a gun barrel might acquire a larger 
permanent magnetic moment than would be 
expected for other structures of similar size 
and weight. 


DETECTION OF LARGE STEEL 
STRUCTURES 

Under favorable conditions large steel struc- 
tures can be detected from altitudes of 3,000 



feet. An example of such a structure might be 
a shipyard, a large steel bridge, or a power 
plant, which would comprise vertical structural 


CONFIDENTIAL 




AN/ASQ AS A NAVIGATIONAL AID 


133 


steel members over 100 feet high. For condi- 
tions to be favorable it should be known that 
magnetic anomalies of geological origin are 
absent in the immediate neighborhood of the 
target and that there are no electrical currents 
creating rapid oscillations of the magnetic field. 
If geological anomalies are present, the signal 
from the target may blend into the deflection 



due to the terrain. Usually enough is known 
about the geology of enemy territory so that 
it would be possible to predict whether or not 
geological anomalies would be troublesome. 
The detection of large steel targets from alti- 
tudes in excess of 500 feet is facilitated by ex- 
tending the low-frequency response of the ASQ 
detector. 

Figure 8 shows signals obtained over the 
Glenwood Power Plant, Long Island, at an alti- 


tude of 3,800 feet. The slow character of the 
recorded deflections indicates that they are 
caused by iron masses rather than by electric 
currents. 

The difficulty in locating a specific structure 
within a city is obvious from Figure 9 which 
shows a pass over the center of Philadelphia at 
1,700 feet. The transients from d-c power lines 
completely obscure the effects from steel masses. 


« 4 DETECTION OF LARGE CITIES 
AND INDUSTRIAL AREAS 

The detection of large cities'^’’ through the 
overcast with ASQ equipment from altitudes 
greater than 3,000 feet depends entirely on the 
rapid magnetic fluctuations created by electric 
currents. The maximum altitude from which a 
large city can be detected by this means is 
about 20,000 feet. Figure 10 shows signals re- 
corded at an altitude of 12,000 feet during the 
Army test flights over the city of Baltimore. 
Records were also obtained over San Diego, 
New York City, Philadelphia, Baltimore, Wash- 
ington, New Haven, and Providence. Hartford 
and Bridgeport, Connecticut, gave no detectable 
signals from 6,000 feet. A night flight over San 
Diego showed much smaller deflections over 
certain parts of the city than were recorded 
during the daytime, which corroborates the de- 
duction that the disturbances are caused by 
d-c power systems. 


AN/ASQ AS A NAVIGATIONAL AID 

The possibility of the use of the ASQ equip- 
ment for navigating bombing aircraft to their 
targets should be mentioned.^^ Magnetic anom- 
alies of geological origin have patterns much 
like topographic patterns in a mountainous re- 
gion. Assume that a navigator is given a topo- 
graphic map of enemy territory and that he 
has an accurate absolute altimeter in addition 
to the barometric altimeter. By plotting terrain 
clearance while flying above the overcast at a 

^ The Naval Ordnance Laboratory also made some 
investigation of the possibility of using MAD for geo- 
physical surveying.®’ ^ 


CONFIDENTIAL 


134 


USE OF MAD FOR LAND TARGETS 


constant barometric altitude, he should be able 
to navigate the aircraft to the target area, pro- 
vided there are some easily identifiable moun- 
tain peaks in its vicinity. 

The ASQ, with a d-c amplifier on the detector, 
can be used in very much the same way with a 
total magnetic intensity contour map taking 
the place of the topographic map. The prepara- 
tion of such a magnetic contour map requires 
a survey of the area by ASQ-equipped recon- 
naissance aircraft. During the survey a record 


is taken of the relative total magnetic intensity 
referred to a given point of departure, and the 
position of the aircraft is determined con- 
tinuously or at intervals by photographs of the 
ground. 

A demonstration magnetic survey flight was 
made from Roosevelt Field into Connecticut at 
an altitude of 12,000 feet, using an ASQ with a 
d-c amplifier on the detector. The purpose was 
to demonstrate that with such equipment mag- 
netic geological anomalies can be mapped to be 
used as fixed airway markers or beacons roughly 
lined up with the geological strike of the area. 


The closed traverse surveyed is shown on the 
map of Figure 11. The circuit CDEGHC was 
flown over twice. The track of the airplane was 
plotted by visual observation of the ground 
without photography or a drift sight and is 
probably in error by plus or minus one mile. 
The difference between the magnetic values ob- 
tained during the two flights around the circuit 
are largely attributable to the failure to fly 
along exactly the same track. Figure 12 is the 
magnetic profile along the loop CDEGHC shown 


on the map of Figure 11. The circled points 
are the readings obtained during the first time 
around the loop. These profiles are similar to 
elevation profiles of the terrain except that it 
is the magnetic elevation that is being plotted. 
Of course, the magnetic intensity does not 
usually bear any relation to the actual to- 
pography, but it does present features fixed 
with respect to the ground. It should be noted 
that to be more effective for survey work, the 
ASQ must be provided with a more stable 
voltage source for supplying the biasing cur- 
rent to the detector. 



CONFIDENTIAL 



GLOSSARY 


AIL. Airborne Instruments Laboratory. 

AM-l/ASQ-1. Detector and amplifier circuits of the 
AN/ASQ-1 system. 

AM-9/ASQ-1A. Control amplifier for the DT-3/ASQ-1A 
and DT-3A/ASQ-1A magnetometer heads. 

AM-36/ASQ. Amplifier for use with the eddy-current 
compensator. 

AN/ASQ-1. The final production model of the MAD 
equipment developed by Airborne Instrument 
Laboratory. 

AN/ASQ-IA. The same as AN/ASQ-1 but using the 
DT-3 or DT-3A universal magnetometer head. 

AN/ASQ-2. A dual installation of AN/ASQ-1 using 
a CM-l unit. 

AN/ASQ-2A. A dual installation of AN/ASQ-IA using 
a CM-l unit. 

AN/ASQ-2B. A dual installation of AN/ASQ-1 using 
a CM-2 unit. 

AN/ASQ-2C. A dual installation of AN/ASQ-IA using 
the CM-2 unit. 

AN/ASQ-3. The production model of the MAD system 
developed by Bell Telephone Laboratories and the 
Naval Ordnance Laboratory. 

ARM. Aviation radioman. 

Barkhausen Discontinuities. The small-scale step- 
wise characteristics of the hysteresis curve for 
ferromagnetic materials. Believed due to sudden 
changes in the magnetization of small “domains” 
within the material. 

BTL. Bell Telephone Laboratory. 

Click Test. A means of quickly checking the overall 
performance and sensitivity of an MAD system. An 
artificial signal is supplied to the system by mo- 
mentarily changing the value of that current which 
neutralizes the effect of the earth’s field on the 
detector magnetometer. 

CM-l/ASQ-2. Lateral indicator and automatic tripper 
unit for use in heavier-than-air craft. 

CM-2/ASQ-2B. Lateral indicator and automatic tripper 
unit for use in lighter-than-air craft. 

CP-2/ASQ-1. Automatic tripper unit for use with 
AN/ASQ-1. 

CU-36/ASQ-2. A switch box for use with CM-l and 
CM-2 units. 

Deperming. The process of removing the permanent 
magnetic moment of a ferromagnetic body. 

DT-l/ASQ-1. Magnetometer head and servo motor as- 
sembly for the AN/ASO-1 system. (The “polar 
head.”) 

DT-lA/ASQ-1. Same as DT-l/ASQ-1 with improved 
antishock mounts. 

DT-3/ASQ-1A. Magnetometer head and servo motor 
assembly suitable for use in all latitudes. (The “uni- 
versal head.”) 

DT-3A/ASQ-1A. Improved model of DT-3/ASQ-1A. 

DY-4/ASQ-1. Power supply for the AN/ASQ-1 system. 

Gamma. A unit of magnetic field strength, equal to 10~5 
oersteds. 

Helmholtz Coils. Two coaxial coils of equal diameter 
spaced in such a manner that current passed through 
them creates a uniform magnetic field over much of 
the volume between the coils. 


HG-7 Head. Magnetometer head used in the Mark IV 
B-2 MAD. 

HG-7A Head. Equivalent to the DT-l/ASQ-1. 

HTA. Heavier-than-air craft. 

“L” Pad. A network of resistors built into a kit for 
use in experimental impedance adjustments. 

LTA. Lighter-than-air craft. 

MABS. Any magnetic airborne bombing system such 
as AN/ASQ-2. 

MAD. Magnetic airborne detection equipment. 

Mark I MAD. MAD model developed at the Gulf Re- 
search and Development Co. 

Mark II MAD. Production model of the Mark I MAD 
developed at Gulf Research and Development Co. 

Mark IV B-1 MAD. First production model of a 
magnetically oriented MAD. 

Mark IV B-2 MAD. Improved production model of 
Mark IV B-1. 

Mark IV B-3 MAD. The Mark IV B-2 system modified 
to use a single-frequency drive for all magnetom- 
eters and with pass band altered for use with auto- 
matic units. 

Mark V MAD. An* experimental model using a mag- 
netically erected gyroscope to orient the detector 
magnetometer. 

Mark VI MAD. The equivalent of the AN/ASQ-1. 

Mark X MAD. Equivalent to AN/ASQ-3. 

Mat- 1. Magnetic attack trainer, original model. 

Mat- 3. Magnetic attack trainer, improved model. 

NOL. Naval Ordnance Laboratory. 

“0” Unit. Forerunner of the CP-2/ASQ-1 tripper. 

“0-1” Unit. Forerunner of the CP-2/ASQ-1 tripper. 

0-1/ASQ-l. Magnetic driver circuits of the AN/ASQ-1 
system. 

Perm. The permanent magnetic moment of a body. 

Permalloy. A series of alloys having high magnetic 
permeability, usually Ni-fe. 

“Q” Unit. Prototype of the TS-7/ASQ. 

Radio Sono Buoy. An automatic device, to be fioated 
on the surface of water, which detects and amplifies 
underwater sounds and broadcasts them in the 
atmosphere by radio. 

RC-132. The Army designation for the Mark IV B-2 
MAD. 

Selsyn Motor. A type of electromagnetic machine, 
which causes a controlled rotation through any de- 
sired angle in response to an electrical signal. 

Spike. A feature of the output voltage curve of the 
MAD magnetometer bridge. See Section 2.2.1. 

Time Index. A feature of an MAD signal record; it is 
the time taken to record the peak of minimum dura- 
tion. See Section 3.6. 

TS-7/ASQ. The control box of the adjustable perm 
compensator. 

TS-160/ASQ-2. Signal simulator for testing CM-l and 
CM-2 units. 

“T” Unit. Forerunner of the CM-l/ASQ-2 unit. 

“U” Unit. Prototype of the AM-9/ASQ-1A. 

“X” Unit. Prototype of the AM-36/ ASQ. 


CONFIDENTIAL 


135 





BIBLIOGRAPHY 


Numbers such as Div. 6-41 1-Ml indicate that the document listed has been microfilmed and that its title 
appears in the microfilm index printed in a separate volume. For access to the index volume and to the 
microfilm, consult the Army or Navy agency listed on the reverse of the half-title page. 

CHAPTER 1 


1. Derivatives of a Dipolar Field, Norman A. Haskell, 
Technical Memorandum 5, CUDWR, Sept. 16, 1941. 

Div. 6-411-Ml 

2-4. Develojmieyit of a Device Responsive to Changes 
in Magnetic Field and Designed to Indicate the 
Approach of Ferromagnetic Objects, Victor V. 
Vacquier, NDCrc-99, Research Project 45P1, Gulf 
Research and Development Company, Apr. 1, 
June 1, July 1, 1941. Div. 6-421-Ml 

5. Results of Magnetic Detection Tests of Submarine 
S-A8 from PBY Plane on October 21, 19 hi, Victor 
V. Vacquier, OEMsr-27, Gulf Research and De- 
velopment Company, Oct. 28, 1941. Div. 6-421-M2 

6. Aircraft Magnetometer, L. D. Palmer and R. D. 

Wyckoff, Gulf Research and Development Com- 
pany, Apr. 7, 1942. Div. 6-421-M3 

7. Application of Sensitive Magnetic Devices to Detec- 

tion of Submarines from Aircraft, OSRD 1870, 
NDRC 6.1-sr27-1107, Gulf Research and Develop- 
ment Company, July 1, 1942. Div. 6-421-M4 

8. Magnetic Airborne Detector Apptaratus for Dif- 

ferential Coil Method, OSRD 885, NDRC C4-sr40- 
084, BTL, June 20, 1942. Div. 6-425-Ml 

9. Test of Performayice of MAD Equiprnent at Key 
West, Florida (with Addeyidum, November 7, 
19U2), L. G. Parratt, Report 661, NOL, Oct. 5, 

1942. 

10. Procedures w Testing the Performance of MAD 
Equipment, L. G. Parratt, Memorandum 2453, 
NOL, Oct. 9, 1942. 

11. Procedures in Testing the Performance of MAD 
Equipment, L. G. Parratt, Memorandum 2567, 
NOL, Nov. 6, 1942. 

12. Magnetic Airboime Detector, Develo^yment of a 

Magnetic Orienting System, NDRC 6.1-sr367-535, 
BTL, Jan. 4, 1943. Div. 6-425-M2 

13. Procedures for Tests of Performance of Magnetic 
Airborne Detection Equipmient, L. G. Parratt, Re- 
port 3110, NOL, Feb. 6, 1943. Div. 6-423.2-M2 

14. Flight Tests of AN ! ASQ-LT A at Lakehurst 17-21 
June 19Jf3, E. M. Hafner, Memorandum 3939, 
NOL, July 1, 1943. 

15. Detection Range of Mk X MAD, Memorandum 
4064, NOL, July 30, 1943. 

16. Development and Description of MAD Types 
AN ! ASQ-3 and 3 A, Report 830, NOL. 

17. Performance and Characteristics of AN f ASQ-1 
and AN / ASQ-3 Equipment, BuShips, May 25, 1943. 

Div. 6-425-M3 

18. Performance of ASQ-1 and ASQ-3 Equipment, 
L. G. Parratt, Memorandum 4104, NOL, Aug. 9, 

1943. 


19. Comparison of Signals from Mk 6 and Mk 10 
MAD, S. E. Forbush, Memorandum 4131, NOL, 
Aug. 17, 1943. 

20. Flight Tests of Production ASQ-3A, E. M. Hafner, 
Memorandum 4714, NOL, Dec. 20, 1943. 

21. Preliminary Design Consider'ations in Maximizing 

Rigidity of Coil-Pair Supjyorts, John N. Adkins, 
AIL, June 25, 1941. Div. 6-412-Ml 

22. {Development of Devices and Methods for Detect- 

ing Submarines by Magnetic Effects'] Rejmrt of 
Work on Contract OEMsr-3^, Albert W. Hull, 
OSRD 1042, NDRC C4-sr34-536, General Electric 
Research Laboratory, Oct. 24, 1942. Div. 6-422-Ml 

23. {Magnetic Airborme Detection] Annual Report 

{for] July 1, 19U2 {to] August 31, 19A3, AIL, Oct. 

1, 1943. Div. 6-401-M2 

24. {Magnetic Airborne Detectioyi Equipment] Annual 

Repiort {for] 19 U2 by Operations and Installation 
De 2 yartment, AIL, 1942. Div. 6-401-Ml 

25. Completion Report, on OSRD Contract OEMsr-20, 
AIL, July 1, 1942 to Aug. 31, 1943. Div. 6-112-Ml 

26. Magnetic Airborne Detection Equi])ment, OSRD 
5486, NDRC 6.1-srll29-1773, AIL, July 15, 1945. 

Div. 6-401-M3 

27. Spinner Typ)e of Magnetic Oy'ientation System, 
Norman E. Klein, AIL, June 20, 1942. 

Div. 6-426-M2 

28. Magnetic Airborne Detector, Mark V, Victor V. 

Vacquier, AIL, Mar. 8, 1943. Div. 6-424-Ml 

29. Magnetically Oriented Magnetic Airborne Detec- 

tion Equipment. Basic Principyles of Design, Otto 
H. Schmitt, NDRC C4-sr20-174, AIL, July 15, 
1942. Div. 6-423-Ml 

30. The Magnetic Airborne Detector, Thomas H. 
Osgood and R. R. Palmer, OSRD 1124, NDRC 
6.1-sr20-664, CUDWR, Dec. 19, 1942. 

Div. 6-423-M3 

31. Descriptive Notes {on] Magnetic Airborne De- 

tector, Mark IV-B2, Jay W. Wright, AIL, Oct. 8, 
1942. Div. 6-423-M2 

32. Insjyection and Accepttance Record Sheets for MAD 
Mark IV-B2, AIL. 

33. The 12-Volt Operation of Mark IV-B2, Russell R. 

Yost, Jr., AIL, Oct. 16, 1942. Div. 6-426-M3 

34. Character'istics of Permalloy Magnetometer Using 

Thyratron Pulse Driver, Walter E. Tolies, AIL, 
Mar. 15, 1943. Div. 6-412-M6 

35. Physical Princijdes of the General Electric Mag- 

netometer, Mine Unit Report 272, NOL, July 22, 
1941. 


CONFIDENTIAL 


137 


138 


BIBLIOGRAPHY 


CHAPTER 

1. Saturated Core Magnetometers, OSRD 5314, NDRC 11. 
6.1-srll29-1772, Service Project NA-120, AIL, 

May 16, 1945. Div. 6-410-M2 

2. Magnetometer Bridge, Walter H. Brattain, AIL, 12. 

Sept. 18, 1943. Div. 6-412-M8 

3. Magnetometer Bridge Balance, Walter H. Brattain, 

AIL, Nov. 26, 1943. Div. 6-412-M9 13. 

4. Unbalance in Heads, Walter H. Brattain, AIL, 

June 8, 1942. Div. 6-423.1-M2 

5. Measuring and Matching of Coils for Magnetic 14. 
Airborne Detector Heads, Arthur C. Weid and 
Max S. Richardson, AIL, Aug. 4, 1942. 

Div. 6-412-M4 

6. The Theory of the Magnetometer Detector, Paul S. 15. 

Lansman, AIL, Mar. 11, 1944. Div. 6-411-M3 

7. Sensitivity of the Permalloy Magnetometer, John 

N. Adkins, AIL, July 13, 1942. Div. 6-413-Ml 16. 

8. A Graphical Explanation of the Behaviour of the 

Saturated Core Magnetometer, Franklin Furst, 17. 
AIL, Sept. 28, 1943. Div. 6-411-M2 

9. Saturated Core Magnetometers, Walter H. 18. 

Brattain, AIL, July 14, 1943. Div. 6-410-Ml 

10. Voltage Sensitivity of the Detector Strips, Arthur 
C. Weid, AIL, Aug. 3, 1943. Div. 6-413-M5 

CHAPTER 

1. Variation of Total Magnetic Field around Sub- 11. 
marines, R. N. Snow, Memorandum 1904, NOL, 

July 25, 1942. 

2. Extrapolation of MAD Dynamic Signatures and 12. 
Detection Range of Mark X MAD at Different 
Altitudes, R. N. Snow, Memorandum 3505, NOL, 13. 
Apr. 13, 1943. 

3. Signatures and Detection Range of MAD Equip- 
ment, S. E. Forbush, Report 734, NOL, Jan. 29, 14. 

1943. 

4. Characteristics of MAD Input Spectra, S. E. 

Forbush, Memorandum 3239, NOL, Mar. 11, 1943. 15. 

5. Preliminary Statement Concerning Apparent 
Obliteration of Noise by Signals, Paul S. Lansman, 

AIL, Sept. 8, 1943. Div. 6-414-M2 

6. Moments of Inertia of Various Mark IV Heads and 

Attending Parts, Norman E. Klein, AIL, Aug. 17, 16. 

1942. Div. 6-423.1-M5 

7. The DT-3 No. One Gimbal Jitter, Henry B. Riblet, 

AIL, Dec. 3, 1943. Div. 6-431.1-M8 17. 

8. Interaction between Orienter and Detector Ele- 
ments, Walter H. Brattain, AIL, May 15, 1942. 

Div. 6-423.1-Ml 18. 

9. Microphonics in Mark IV-Bl Equipment, Russell 

R. Yost, Jr., AIL, July 15, 1942. Div. 6-423.2-Ml 19. 

10. Handbook of Maintenance Instructions for 
AN ! ASQ-1 and AN / ASQ-lA Equi^rment, Hand- 
book CO-AN-08-20-5, U. S. War and Navy De- 20. 
partments and the Air Council of the United 
Kingdom, Sept. 22, 1943. Div. 6-431-M2 


2 

Magnetic Airborne Detector. Investigation of Mag- 
netic Noise, NDRC 6.1-sr967-llll, BTL, Oct. 14, 
1943. Div. 6-414-M3 

Magnetic Airborne Detector. Investigation of Mag- 
netic Noise (Supplemental Rejjort), OSRD 3148, 
NDRC 6.1-sr967-1320, BTL. Div. 6-414-M6 

Noise in Magnetic Airborne Detection Equipment 
and the Signal-to-N oise Ratio, Karl S. Packard, 
AIL, Dec. 8, 1943. Div. 6-414-M4 

Technique Used in Assembly of Coils and Mag- 
netic Elements in Magnetic Airborne Detector, 
Mark IV-B, Walter H. Brattain, AIL, May 11, 
1942. Div. 6-412-M2 

Sorting of Magnetic Strips, Arthur C. Weid and 
Max S. Richardson, AIL, Aug. 4, 1942. 

Div. 6-412-M3 

Ceramic Moiinting for Detector Elemeyits, Karl S. 
Packard, AIL, Aug. 31, 1943. Div. 6-412-M7 

Heads, Walter H. Brattain, AIL, Aug. 6, 1942. 

Div. 6-423.1-M4 

Technique Used in Assembly of Coils and Mag- 
netic Cores in Magnetic Airborne Detector, Mark 
IV-B Heads, Arthur C. Weid and Max S. Richard- 
son, AIL, Aug. 4, 1942. Div. 6-41 2-M5 


3 

[T/ie] AN ! ASO-1 Magnetic Airborne Detection 
Equipment, OSRD 2035, NDRC 6.1-S3280-813, 
AIL, Oct. 19, 1943. Div. 6-431-M3 

Misalignment of Detector Elements, John N. 
Adkins, AIL, June 10, 1942. Div. 6-423. 1-M3 

Frequeney Response Measurements of Mark VI 
Equipollent, C. Richard Evans and Lyman C. Ihrig, 
AIL. Div. 6-431-M4 

Maintenance and 6K5 Tube Selection for Mag- 
netic Airborne Deteetor, Mark IV-B2, AIL. 

Div. 6-423.2-M4 

Perfoi'mance of Mark VI Magnetic Airborne De- 
tection Equipment on Planes of First Sea Seareh 
Attack Grouj), USAAF, at Key West, Florida, 
May 16 [to] 26, 19 U3, Winfield E. Fromm, AIL, 

May 29, 1943. Div. 6-431-Ml 

The Latitude of Magnetic Airborne Detector, Mark 
VI, Milford C. Jensen and Carl P. Swinnerton, 
AIL. Div. 6-431-M5 

The Vibration Equipment of Airborne Instruments 
Laboratory, R. F. Norris, AIL, Feb. 5, 1944. 

Div. 6-462-M3 

Magnetometer Orientation Suspensions, Norman E. 
Klein, AIL, December 1943. Div. 6-431. 1-M7 

Magnetometer Suspensions, OSRD 5051, NDRC 
6.1-srll29-1771, AIL, May 7, 1945. 

Div. 6-431. 1-M9 

The High Bank-Angle Problem in the Design of 
MAD Equipment, P. M. Murphy, Memorandum 
4263, NOL, Sept. 11, 1943. 


CONFIDENTIAL 


BIBLIOGRAPHY 


139 


21. Universal Head, Norman E. Klein, AIL, Mar. 22, 

1943. Div. 6-431. 1-M2 

22. Equatorial Head Construction, Norman E. Klein, 25 

AIL, Jan. 25, 1943. Div. 6-431.1-Ml 

23. Analysis of Operation of the Universal Mag- 
netometer Head, Max S. Richardson and Arthur C. 

Weid, NDRC 6.1-sr20-806, AIL, Aug. 19, 1943. 

Div. 6-431.1-M4 26. 

24. A General Type of Operation of the Univei'sal 
Magnetometer Head, Max S. Richardson and 


CHAPTER 

1. Exercises u'ith Submarme S-44, 750 Ton, Elwyne 
M. Mulherin, AIL, Feb. 19, 1943. Div. 6-443-M2 

2. Measurement above Submarines, William B. 10. 

Lodge, AIL, Apr. 27, 1943. Div. 6-441-M3 

3. Estimate of Magnetic Moments of U-boats At- 11. 
tacked March 16 and May 15, 19^4. by VP-63, 
George W. Morton, AIL, July 12, 1944. 

Div. 6-441-M4 12. 

4. Laboratory Method for Investigation of Sub- 
marine Magnetic Field Patterns, Otto H. Schmitt 

and Viola E. Schmitt, NDRC 6.1-sr20-844, AIL, 13. 
Apr. 23, 1943. Div. 6-441-M2 

5. Magnetic Field Patterns above Submarines, Parts 

1 and 2, Otto H. Schmitt, Viola E. Schmitt, and 14. 
others, NDRC 6.1-sr20-845, AIL, Apr. 5, 1943. 

Div. 6-441-Ml 

6. Theoretical Consideration of AN / ASQ-1 Signals. 

An Appendix to Experimental Study of ASQ-1 
Signals, NDRC 6.1-srll29-1387a, AIL, Nov. 4, 15. 

1944. Div. 6-442-M8 

7. Dynamic Signals, James T. Wilson, AIL, Aug. 6, 16. 

1943. Div. 6-442-M4 

8. Experimental Study of AN ! ASQ-1 Signals 

(Volumes lA to IVA and IB to IVB), NDRC 6.1- 17. 

srll29-1387, AIL, June 10, 1944. Div. 6-442-M7 

9. Statistical Study of AN / ASQ-1 Signal Data. An 
Appendix to Experimental Study of AN ! ASQ-1 


CHAPTER 

1. MAD Development, Dual System for Indicating 6. 
Direction and/or Depth, L. G. Parratt, Memoran- 
dum 2811, NOL, Dec. 19, 1942. 

2. Limitations on the Value of Dual MAD, R. N. 7. 
Snow and others. Memorandum 4279, NOL, Dec. 

1, 1943. 8. 

3. Lateral Width of a Track Over a Peak as Deter- 

mined by the Ratio: Sum to Difference, P. E. 
Martin, AIL, June 16, 1943. Div. 6-442-M3 9. 

4. Notes on Automatic Lateral Control for Vertical 
Bombs, James H. Stein, AIL, Mar. 8, 1943. 

Div. 6-432.2-Ml 10. 

5. Rayige Variations and Lateral Ey'rors in Inferred 

Target Position, John N. Adkins, AIL, January 11. 
1943. Div. 6-442-Ml 


Arthur C. Weid, NDRC 6.1-S3280-810, AIL, Sept. 
28, 1943. Div. 6-431.1-M5 

Operation of the Universal Magnetometer Head 
with Linear Non-Ideal Control Mechanism, Max S. 
Richardson and Arthur C. Weid, NDRC 6.1- 
S3280-812, AIL, Sept. 30, 1943. Div. 6-431.1-M6 
Final Report, Magnetic Anomaly Detector, First 
Sea Search Attack Group, USAAF, Langley Field, 
Va., SS No. 7. 


4 

Signals, NDRC 6.1-srll29-1387b, AIL, Nov. 4, 
1944. Div. 6-442-M9 

Peak Position Charts for 50° Dip, John N. Adkins, 
AIL, Feb. 18, 1943. Div. 6-442-M2 

Automatic Retro-bombing in Regions of High Dip 
Angle, John N. Adkins, AIL, May 25, 1943. 

Div. 6-443-M3 

Signal Recognition Manual, AN / ASQ-1 and 
AN/ASQ-lA in Airplanes, OSRD 3630, NDRC 
6.1-srll29-1383, AIL, Apr. 6, 1944. Div. 6-442-M6 
Signal Recognition Manual, Magnetic Airborne 
Detector, Type IV-B2 in Airships, NDRC 6.1- 
srll29-820, AIL, Dec. 20, 1943. Div. 6-442-M5 
Relative Effectiveness of Different Barrage Pat- 
terns for Aircraft Retro-Contact Rocket Bombs, 
Fired on Magnetic Airborne Detection Contact, 
Leonard 1. Schiff and W. H. Wilson, NDRC C4- 
sr20-207, CUDWR, Aug. 4, 1942. Div. 6-443-Ml 
Tactical Use of the Magnetic Airborne Detector, 
AIL, July 13, 1943. Div. 6-443-M4 

Effect of Wind on Magnetic Airborne Detection 
Tactics, Judson Mead, AIL, Feb. 1, 1944. 

Div. 6-443-M5 

U-Boat Contact and Attack by VP-63, February 
24, 1944 (with Appendix by J. T. Wilson, April 
26, 1944). Edmond W. Westrick, AIL, Apr. 1, 
1944. Div. 6-402-M4 


5 

Routine Measurements of Frequency and Phase 
Response of Detector Units, Reuben A. Isberg, 
AIL, Mar. 10, 1943. Div. 6-423.2-M3 

Sensitivity Instability in May'k VI Equipment, 
Jay W. Wright, AIL, Apr. 9, 1943. Div. 6-413-M2 
Relative Sensitivity of Paired May'k VI Units for 
Dual Opey'ation, Jay W. Wright, AIL, Apr. 21, 
1943. Div. 6-413-M3 

Stability of Sensitivity of Mark VI Units to he 
Used in Conjunction with T -Units, Jay W. Wright, 
AIL, Apr. 28, 1943. Div. 6-413-M4 

Tripper Units, Jay W. Wright, AIL, May 10, 
1943. Div. 6-432.2-M2 

Ty'ipper Research, Report of Project 311, Cutler 
R. Miller, AIL, Aug. 18, 1943. Div. 6-432.2-M5 


CONFIDENTIAL 


140 


BIBLIOGRAPHY 


12. Notes on Peak Tripper Circuits for Use with Mark 
IV-B2, James H. Stein, AIL, Jan. 5, 1943. 

Div. 6-432.1-Ml 

13. Frequency Discriminating Network Used in CP-2 
and CM-ly John N. Adkins, AIL, Oct. 27, 1943. 

Div. 6-432.1-M2 

14. Flight Tests of CM-1 ! ASQ-2 in B-24^ at Langley 

Field July 12 [to] July 17, 194-S, Judson Mead, 
AIL, July 27, 1943. Div. 6-432.2-M3 


15. Residts of Tests oyi the CM-1 ! ASQ-2 Unit, Russell 

R. Yost, Jr. and Julius Hetland, AIL, July 31, 
1943. . Div. 6-432.2-M4 

16. Installation of AN / ASQ-2A in PBM-3S, Donald 

B. Lee, AIL, Feb. 19, 1944. Div. 6-432.2-M6 

17. Handbook of Maintenance Instructions for CP- 
2/ASQ-l and CP-21 ASQ-lA Equipment, NDRC 
6.1-srll29-1386, AIL, May 12, 1944. 

Div. 6-432.1-M3 


CHAPTER 6 


1. Maneuver Noise in Universal Head, Walter H. 
Brattain, AIL, Apr. 23, 1943. Div. 6-431. 1-M3 

2. Compensation of Magnetic Fields in Magnetic Air- 

borne Detection Equipjyed Aircraft, Walter E. 
Tolies and Victor V. Vacquier, NDRC 6.1-srll29- 
1393, AIL, July 24, 1944. Div. 6-451-M2 

3. Origin and Reduction of Maneuver Noise in Mag- 
netic Airborne Detection Equipped Aircraft, R. A. 
Peterson, NDRC 6.1-sr20-317, AIL, Mar. 25, 1943. 

Div. 6-451-Ml 

4. Compensation of Induced Magnetic Fields in Mag- 

netic Ah'borne Detection Equipped Aircraft, 
Walter E. Tolies, NDRC 6.1-sr20-320, AIL, Apr. 

21, 1943. Div. 6-451.1-M3 

5. Compensation of TT and V Maneuver Signal in 

Magnetic Airborne Detection Equipped Aircraft 
with V Maneuver Signals, William R. Keye, AIL, 
Mar. 17, 1944. Div. 6-451.1-M13 

6. General Solution for Angular Position of Com- 

pensation Magnets, P. V. Dimock, AIL, Sept. 2, 
1943. Div. 6-451.1-M7 

7. Compensation of ASQ-2 Installation in K-3 Blimp, 

Victor V. Vacquier, AIL, Sept. 7, 1943. 

Div. 6-451.1-M8 

8. Compensation of ASQ-2 Installation in Blimp K-7, 
Victor V. Vacquier, AIL, Oct. 8, 1943. 

Div. 6-451. 1-M9 

9. Electronic Perm and Induced Compensation, 
Russell R. Yost, Jr., AIL, May 12, 1943. 

Div. 6-451.1-M4 

10. Deperming Procedure, R. G. Madsen, AIL, Dec. 23, 

1943. Div. 6-451.1-Mll 

11. Magnetic Survey of PBY Float X-Frame, 
Edmond A. Westrick, AIL, May 17, 1943. 

Div. 6-451. 1-M5 

12. Compensation of Navy Boat PC-64, at Main Pier, 

Sandy Hook, N. J., John N. Adkins and T. H. 
Johnson, AIL, May 26, 1942. Div. 6-451. 1-M2 

13. Compensation of B-18M 6288 at Runway in Front 
of Hangar 6, Mitchell Field, John N. Adkins and 
T. H. Johnson, AIL, May 15, 1942. Div. 6-451.1-Ml 

14. Study and Neutralization of the Magnetic Field of 

PBY -5 A 9UP7, by Peterson, Adkins, Stein, and 
Blomquist at Quonset Point, John N. Adkins, 
AIL. Div. 6-451. 1-M14 

15. Magnetic Measurements of the TBF Parts Made 


at Naval Air Station, Quonset Point, Walter E. 
Tolies, AIL, Dec. 10, 1943. Div. 6-451.1-MlO 

16. Py'ocedure for Approximate Adjustments of the 

Transverse and Longitudinal Perm Compensating 
Fields on the Ground, William R. Keye, AIL, Jan. 
26, 1944. Div. 6-451.1-M12 

17. Flight Tests of Permalloy Compensators for PBY 

Tail Cones, Victor V. Vacquier, AIL, June 15, 

1943. Div. 6-451.1-M6 

18. Analysis of Data Supplied by the Alhambra 
Laboratory Concerning the Eddy Currents in 
PBY Wing, Walter E. Tolies, AIL, Feb. 5, 1944. 

Div. 6-451.2-M3 

19. Test of Eddy-Current Disturbance from histim- 

ment Support on PBM Wing, Victor V. Vacquier, 
AIL, Sept. 3, 1943. Div. 6-451.2-Ml 

20. Eddy-Current Effect from PBM Fairing, Victor V. 

Vacquier, AIL, Sept. 9, 1943. Div. 6-451. 2-M2 

21. Study of TBF Eddy Current Compensation, 
William R. Keye, AIL, Mar. 24, 1944. 

Div. 6-451. 2-M4 

22. Compensation of the PBY Dual Wing Installation, 
William R. Keye, AIL, May 27, 1944. 

Div. 6-451.3-M7 

23. Compensation of PBY Tail Cone Installation, 
William R. Keye, AIL, May 18, 1944. 

Div. 6-451.3-M6 

24. Magnetic Compensation for Magnetic Airborne De- 

tection Aircraft Installations, R. A. Peterson and 
Orrin W. Towner, NDRC 6.1-sr20-309, AIL, Dec. 
14, 1942. Div. 6-451.3-Ml 

25. Mark VI Magnetic Airborne Detection Installation 
in Stinson 10- A Airplane AAF Designation L-9B, 
No. 42-94136, Victor V. Graf, AIL, Mar. 16, 1943. 

Div. 6-451.3-M2 

26. Procedure for PBM Magnetic Compensation, H. N. 

Jacobs, AIL, Apr. 15, 1944. Div. 6-451. 3-M5 

27. Compensation of AN I ASQ-2 Installation in Army 

B-18 Bomber No. 7470, Victor V. Vacquier and 
Walter E. Tolies, NDRC 6.1-S3280-816, AIL, Oct. 
30, 1943. Div. 6-451. 3-M4 

28. Supplement to Magnetic Compensation of VP-91, 

August 21, 1943, Walter E. Tolies, AIL, Sept. 22, 
1943. Div. 6-451.3-M3 

29. The Compensation of One Component of Induced 

Magnetism, Wilmer C. Anderson, AIL, Mar. 15, 
1943. Div. 6-451.4-Ml 


CONFIDENTIAL 


BIBLIOGRAPHY 


141 


30. Eddy-Curi'ent Compensation, H. N. Jacobs and 
R. I. Strough, AIL, Apr. 29, 1943. Div. 6-451.4-M2 

31. Handbook of Instructions for AN-36 1 ASQ, NDRC 
6.1-srll29-1763, AIL, Sept. 11, 1944. 

’ Div. 6-451.4-M7 

32. Proposed Improvement of Eddy Current Comjjen- 

sation Amplifier, Walter E. Tolies and William R. 
Keye, AIL, Dec. 23, 1943. Div. 6-451.4-M3 

33. Electronic Compensation of an Eddy-Current 
Field in Magnetic Airborne Detectioyi Equipped 
Aircraft Using a Single-Channel Electronic Am- 
plifier with One Input and One Output Coil, 
William R. Keye, AIL, Mar. 10, 1944. 

Div. 6-451.4-M5 

34. The Electronic DC Magnetometer, Philip N. Smith, 

AIL, Jan. 29, 1944. Div. 6-451.4-M4 

35. Technical Specifications for a Transverse Mag- 
netometer Gradiometer, F. L. Johnson and F. M. 
Mayes, Memorandum 3495, NOL, Apr. 10, 1943. 

36. Low Sensitivity Magnetometer, K. A. McLeod, 

AIL, June 13, 1944. Div. 6-451. 4-M6 

37. Detection of Subinerged Submarines from Aircraft, 
Characteristics of AN ! ASQ Birds, Memorandum 


3912, NOL, June 26, 1943 (Revised Aug. 9, 1943). 

38. MAD Installation in TBF Aircraft, 7A2, L. G. 
Parratt, Memorandum 4565, NOL, Nov. 17, 1943. 

39. ASQ-3 Equipment, Initial Service Installation in 
the TBF-lC Airplane, A. J. Tickner, Memorandum 
5134, NOL, Mar. 14, 1944. 

40. The Towed Birdie, Judson Mead and Robert T. 
Knapp, NDRC 6.1-sr20-705, AIL, Apr. 28, 1943. 

Div. 6-452-Ml 

41. Towed Birdie Investigation, Philip N. Smith, AIL, 

Oct. 26, 1943. Div. 6-452-M2 

42. The Towed Bird, Mechanical Details, Philip N. 

Smith, AIL, Feb. 19, 1944. Div. 6-452-M3 

43. Magnetic Airborne Detection Performance Data 
Duj'ing Operation of VP-91 at Kaneohe Bay, 
Oahu, T. H., August lU [to] September U, 19^3, 
Winfield E. Fromm, CUDWR, Sept. 11, 1943. 

Div. 6-402-Ml 

44. Rep>ort of Trip to Kaneohe Bay, Oahu, T. H. with 
VP-91, Walter E. Tolies, AIL, Sept. 25, 1943. 

Div. 6-402-M3 

45. VP-91, August 18 to September 13 [1943], Walter 

E. Tolies, AIL, Sept. 25, 1943. Div. 6-402-M2 


1 . 

2 . 


4. 

5. 

6 . 

7. 

8 . 

9. 

10 . 

11 . 

12 . 

13. 

14. 


CHAPTER 7 


Magnetic Attack Trainer, MAT-3, NDRC 6.1- 
srll29-1764, AIL, Oct. 9, 1944. Div. 6-461-M6 
Handbook of Instructions [/or] MAT-3 (Volumes 
A, B, ayid C), Service Project NA-120, AIL. 

Div. 6-461-M8 

Magnetic Attack Trainer, NDRC 6.1-srll29-825, 
AIL, Feb. 16, 1944. Div. 6-461-M3 

Universal Motor and Control System for MAT-3 
and MAT-A, W. A. Fails, AIL. Div. 6-461-M9 
Remote View Optical System for the Attack 
Trainer, W. B. Greenlee, AIL, Aug. 30, 1943. 

Div. 6-461-M2 

Magnetic Airborne Detection, Operator’s Short 
Course, James M. Snodgrass, AIL. Div. 6-461-M7 
Self-Propelled Magnetic Target, John N. Adkins, 
AIL, Mar. 29, 1943. Div. 6-461-Ml 

Towed Magnetic Submarine Simulator, NDRC 
6.1-srll29-1398, AIL, July 22, 1944. 

Div. 6-461-M4 

Pantograph-Type Attack Trainer, NDRC 6.1- 
srll29-1380, AIL, July 26, 1944. Div. 6-461-M5 
JfOO Cycle Motors for HG Assemblies, Jay W. 
Wright, AIL, Mar. 31, 1943. Div. 6-426-M5 

Noise Rejector for 0-Unit, James H. Stein, AIL, 
May 4, 1943. Div. 6-414-Ml 

Jacobs Right-Left Indicator, Jay W. Wright, AIL, 
Jan. 1, 1943. Div. 6-426-M4 

Duplex Detector and Orientor Amplifier Channels, 

Otto H. Schmitt, CUDWR. Div. 6-426-M12 

Proposed Magnetometer Which Does Not Require 
Orientation, W. B. Greenlee, AIL, Oct. 12, 1943. 

Div. 6-426-M7 


15. Magnetic Airborne Detection System. Tests on 
Compensating System, E. P. Felch and T. Slonc- 
zewski. Report 2110-EPF-ML, BTL, May 27, 1942. 

Div. 6-426-Ml 

16. Wave Train Magnetometer, Walter H. Brattain, 

AIL, Dec. 4, 1943. Div. 6-426-M9 

17. Dzwon’s Q-Stabilized Oscillator and Differential 
Detector, Judson Mead, AIL, Mar. 3, 1944. 

Div. 6-426-MlO 

18. Investigation of Effect of Frequency and Phase 

Discrimination on Character of Magnetic Airborne 
Detection Signals, C. Richard Evans and Lyman 
C. Ihrig, AIL, Oct. 15, 1943. Div. 6-426-M8 

19. Analysis of the Parallel-T Network and How It 

Differs from the Analysis of the Wien Bridge 
though Both Accomplish the Same Pur^yose, 
Winston C. Backstrand, AIL. Div. 426-Mll 

20. RC Filters, James T. Wilson, AIL, Sept. 6, 1943. 

Div. 6-426-M6 

21. A Study of Short-Time Fluctuations in the Mag- 
netic Field of the Earth, NDRC 6.1-srll29-1769, 
Service Project NA-120, AIL, Feb. 7, 1945. 

Div. 6-444-Ml 

22. [The Apparatus Used in Measuring the Fluctua- 
tions of the Earth’s Magnetic Field'], Project No. 
323, M. R. Winkler, CUDWR. Div. 6-444-M2 

23. Secondary Effect from Helmholtz Coils, W. B. 

Greenlee, AIL. Div. 6-414-M5 

24. Magnetic Screening by Thin Shields, Paul S. Lans- 

man, AIL, Jan. 21, 1944. Div. 6-462-M2 

25. Standard Magnets, William R. Keye, AIL, July 

21, 1943. Div. 6-462-Ml 


CONFIDENTIAL 


142 


BIBLIOGRAPHY 


CHAPTER 8 


1. [Equipment for the Detection of Objects Other 
Than Submarines'], Report on Project NA-H3, 
NDRC 6.1-srll29-826, AIL, Feb. 16, 1944. 

Div. 6-470-M4 

2. [Equipment for the Detection of Objects Other 

Than Submarines], Report on Project NA-lJf3 (Ex- 
tension), NDRC 6.1-srll29-826a, AIL, Feb. 7, 
1945. Div. 6-470-M7 

3. [Investigation of the Use of AN I ASQ-1 A in De- 

tection of Magnetic Land Targets], Report on 
Project AC-82, NDRC 6.1-srll29-1768, AIL, Feb. 
7, 1945. Div. 6-470-M6 

4. Detection of Armored Vehicles with AN/ASQ-IA 

in B-25H Aircraft No. 3^535, James H. Stein and 
P. N. Schwartz, NDRC 6.1-srll29-1844, AIL, Aug. 
26, 1944. Div. 6-470-M5 


5. Signatures of Moving Vehicles, James T. Wilson, 

AIL, July 9, 1943. Div. 6-470-Ml 

6 . Suggestions for the Use of Magnetic Airborne 
Detection for Bombing Through Overcast, Victor 
V. Vacquier, AIL, Sept. 27, 1943. Div. 6-470-M2 

7. Bombing Through Overcast Report for Flight of 

January 19, 19^4, K. A. McLeod, AIL, Feb. 10, 
1944. Div. 6-470-M3 

8 . Report on Tests of Geophysical Application of 
ASQ-3A Equipment, H. Jensen, Memorandum 
6451, NOL, Dec. 19, 1944. 

9. Geophysical Surveying with the MAD, Report 
937, NOL, May 1, 1945. 

10. Profile of Earth’s Total Magnetic Field from 
Jacksonville to New London, E. M. Hafner, Mem- 
orandum 6016, NOL, Sept. 8, 1944. 


CONFIDENTIAL 


PRINCIPAL PATENT APPLICATIONS AND INVENTION REPORTS FILED UNDER OSRD 

CONTRACTS CONNECTED WITH MAD 


Contract OEMsr — 20 
Contractor: Columbia University 
Airborne Instruments Laboratory 


Inventor 

Title 

Serial Number 

Filed 

Donald G. C. Hare 

Magnetic Stabilization System 

529,003 

3/31/44 

Victor V. Vacquier 

John N. Adkins 

Directional Indicator System 

531,422 

4/17/44 

Otto H. Schmitt 

Compensated Amplifier 

521,599 

2/8/44 

James H. Stein 

Bombing Control 

543,505 

7/4/44 

Otto H. Schmitt 

Unbalanced Magnetometer 

516,612 

1/1/44 

Henry B. Riblet 

Balanced Magnetometer 

534,961 

5/10/44 

Otto H. Schmitt 

Detection System 

531,624 

4/18/44 

Otto H. Schmitt 

Orientation System 

532,144 

4/21/44 

Norman E. Klein 

Orientation System 

543,696 

116/U 

Donald G. C. Hare 

Magnetic Incremometer or Gradiometer 

532,153 

4/21/44 

Otto H. Schmitt 

Phase Shifter 

551,241 

8/25/44 

Donald G. C. Hare 

Filter Network 

535,161 

5/11/44 

Otto H. Schmitt 

Torque Amplifier 

534,980 

5/10/44 

Otto H, Schmitt 

Magnetometer Compensation System 

542,379 

6/27/44 

Richard Evans 

Compensated Magnetometer 

543,700 

7/6/44 

Norman E. Klein 

Magnetic Orientation System 

535,160 

5/11/44 

William L L. Wu 

Automatic Release and Reset System 

543,494 

IIAIU 

Otto H. Schmitt 

Improved Galvanometer 

535,162 

5/11/44 

W. H. Brattain 

N. E. Klein 

M. S. Richardson 

Magnetometer Head 

535,158 

5/11/44 

Otto H. Schmitt 

John H. Hidy 

Bridge Compensation System 

542,658 

6/29/44 

Otto H. Schmitt 

Training System 

548,487 

8/7/44 

Max S. Richardson 

Magnetometer System 

543,923 

7/7/44 

Otto H. Schmitt 

Method of Magnetic Investigation 

548,492 

8/7/44 

Otto H. Schmitt 

Wm. B. Greenlee 

Control System 

543,592 

7/5/44 

Edgar W. Adams, Jr. 
Otto H. Schmitt 

E. G. Sorensen 

Recording Method 

Indicating System 

543,586 

7/5/44 

Otto H. Schmitt 

Motor Control 

543,477 

7/4/44 

James H. Stein 

Wide-Latitude Magnetometer 

535,159 

5/11/44 

Walter H. Brattain 

Wave-Train Magnetometer 

543,924 

imu 

Ralph F. Norris 

Robert D. Avery 

Shock Mounting 

560,450 

10/26/44 

Otto H. Schmitt 

Earl G. Sorensen 

Translation System 

547,478 

7/31/44 

Robert I. Strough 
Harry N. Jacobs 

Eddy-Current Compensator 

542,588 

6/28/44 

Edgar W. Adams, Jr. 

Recording Method 

550,323 

8/19/44 

Otto H. Schmitt 

G. S. Dzwons 

Bomb Simulator 

558,408 

10/12/44 

Otto H. Schmitt 

Tripper System 

547,477 

7/31/44 

Norman E. Klein 
Walter H. Brattain 

Integral-Driven Magnetometer Head 

543,697 

ll&IU 

James H. Stein 

Selective Automatic Missile Release 

548,578 

8/8/44 

Wilmer C. Anderson 

Magnetometer System 

542,493 

6/28/44 

Otto H. Schmitt 

Otto H. Schmitt 

Self-Oscillating Magnetometer 

Demodulator 

542,844 

6/30/44 

Otto H. Schmitt 

Combination Magnetometer and Gradiometer 

555,538 

9/23/44 


CONFIDENTIAL 


143 


PRINCIPAL PATENT APPLICATIONS AND INVENTION REPORTS FILED UNDER OSRD 
CONTRACTS CONNECTED WITH MAD— {Continued) 


Inventor 

Title 

Serial Number 

Filed 

Wilmer C. Anderson 

Induced Magnetization Compensator 

547,448 

7/31/44 

Robert L Strough 
Walter E. Tolies 

Eddy-Current Compensator 

549,433 

8/14/44 

William 1. L. Wu 

Electronic Switching Detection System 

549,435 

8/14/44 

William I. L. Wu 

Adjustable Orientation System 

549,434 

8/14/44 

Victor V. Vacquier 
Walter E. Tolies 

Compensation of Inductance Magnetic Fields 

547,447 

7/31/44 

Walter E. Tolies 

Product-Taking System 

551,238 

8/25/44 

Walter E. Tolies 

Magnetic Field Compensation System 

548,579 

8/8/44 

James H. Stein 

Maneuver Monitor 

548,577 

8/8/44 

Otto H. Schmitt 

Phase-Shift Magnetometer 

548,488 

8/7/44 

Wilmer C. Anderson 

Compensator for Induced Magnetic Field 

547,449 

7/31/44 

Otto H. Schmitt 

Magnetometer 

548,485 

8/7/44 

Otto H. Schmitt 

Dual Amplification System 

548,491 

8/7/44 

Otto H. Schmitt 

Voltage-Regulator System 

548,486 

8/7/44 

Otto H. Schmitt 

Thermal Demodulator 

548,489 

8/7/44 

Otto H. Schmitt 

Varistor Demodulator 

548,490 

8/7/44 

Ralph D. Wyckoff 

Contract OEMsr — 27 

Contractor: Gulf Research & Development Company 
Air-Jet Apparatus for Orienting and Stabilizing Apparatus 

603,309 

7/5/45 

Albert W. Hull 

Contract OEMsr — 34 

Contractor: General Electric Company 

Methods and System for Magnetic Field Investigation 

479,713 

3/19/43 

Victor Vacquier 

Contract NDCrc — 99 

Contractor: Gulf Research & Development Company 
Apparatus for and Methods of Responding to Magnetic 

403,455 

7/21/41 

Victor V. Vacquier 

Fields 

Method and Apparatus for Measuring the Values of 

508,550 

11/1/43 

Gary Muffly 

Edwin P. Felch, Jr. 

Magnetic Field 

Contract OEMsr — 367 

Contractor: Western Electric Company 

Magnetic Field Strength Indicator 

483,754 

4/20/43 

Thaddeus Slonczewski 
Edwin P. Felch, Jr. 

Magnetic Field Strength Indicator 

483,755 

4/20/43 

Thaddeus Slonczewski 
Thaddeus Slonczewski 

Magnetic Field Strength Indicator 

483,756 

4/20/43 

Winthrop J. Means 

Orienting Device 

496,833 

7/30/43 

Thaddeus Slonczewski 

Detection System 

618,551 

9/25/45 

A. G. Laird 

Contract OEMsr — 967 

Contractor: Western Electric Company 

Magnetic Field Detector 

555,058 

9/21/44 

T. Slonczewski 

Donald G. C. Hare 
Donald G. C. Hare 
Donald G. C. Hare 
George S. Dzwons 

Contract OEMsr — 1129 

Contractor: Columbia University 

Airborne Instruments Laboratory 

Inverse Modulation Detector 

Low-Frequency Amplifier 

Compensated Locator 

Stabilized Amplifier 

558,413 

10/12/44 

Otto H. Schmitt 

Oscillator 

549,524 

8/15/44 

Otto H. Schmitt 

Wave-Train Detector 

549,450 

8/14/44 

Walter E. Tolies 

Eddy-Current Compensation 

550,415 

8/21/44 


144 


CONFIDENTIAL 


PRINCIPAL 

PATENT APPLICATIONS AND INVENTION REPORTS FILED UNDER OSRD 
CONTRACTS CONNECTED WITH UKD— {Continued) 

Inventor 

Title 

Serial Number 

Filed 

Wesley A. Fails 

Position Indicator 



Jay W. Wright 

Signal Recognition Trainer 



Otto H. Schmitt 

Noise Generator 

550,476 

8/21/44 

Otto H. Schmitt 

Recording Indicators 

551,242 

8/25/44 

Wilmer C. Anderson 

Magnetometer Compass 

551,173 

8/25/44 

Otto H, Schmitt 

Flight Trainer 

559,784 

10/21/44 

Norman E. Klein 

Planetary Movement 

551,236 

8/25/44 

Donald G. C. Hare 

Emission Stabilized Amplifier 

574,592 

1/25/45 

Donald G. C. Hare 

Sonic Tiltometer 

578,772 

2/19/45 

Wilmer C. Anderson 

Tiltometer System 

578,771 

2/19/45 

Walter E. Tolies 

Compensation of Aircraft Magnetic Fields 

552,516 

9/2/44 

James H. Stein 

Antihunt System 

560,460 

10/26/44 

Wilmer C. Anderson 

Improved Magnetometer Compass 

567,394 

12/9/44 

Kenneth A. McLeod 

Portable Magnetometer 

583,747 

3/20/45 

Russell R. Yost, Jr. 

Gain Control 

613,147 

8/28/45 

Robert F. Schulz 

Improved Fluzmeter-Recorder 



Russell R. Yost, Jr. 




Otto H. Schmitt 

Stabilized Oscillator 




CONFIDENTIAL 


145 


CONTRACT NUMBERS, CONTRACTORS, AND SUBJECT OF CONTRACTS 


Contract 

Number 

Name and Address of Contractor 

Subject 

OEMsr-20 

The Trustees of Columbia University in the 
City of New York 

New York, N. Y. 

Studies and experimental investigations in 
connection with and for the development 
of equipment and methods pertaining to 
submarine warfare. 

OEMsr-1129 

The Trustees of Columbia University in the 
City of New York 

New York, N. Y. 

Conduct studies and experimental investiga- 
tions in connection with the development 
and research work involving the applica- 
tion of magnetic methods to anti-sub- 
marine warfare including the develop- 
ment of airborne equipment and methods 
for training personnel in the use of such 
magnetic methods, establishing the neces- 
sary laboratories and facilities for this 
purpose. 

OEMsr-40 

Western Electric Company, Inc. 

New York, N. Y. 

Experimental studies and investigations of 
the development of equipment and 
methods for detection of submarines by 
magnetic effects. 

OEMsr-367 

Western Electric Company, Inc. 

New York, N. Y. 

Studies and experimental investigations in 
connection with the detection of sub- 
marines by magnetic methods. 

OEMsr-967 

Western Electric Company, Inc. 

New York, N. Y. 

Studies and experimental investigation in 
connection with the phenomenon of MAD. 

OEMsr-34 

General Electric Company 

Schenectady, N. Y. 

Development of equipment and methods for 
detection of submarines by magnetic 
effects. 

OEMsr-27 

Gulf Research and Development Company 
Pittsburgh, Pa. 

Studies and experimental investigations in 
connection with the development of equip- 
ment and methods applicable to the de- 
tection of submarines by magnetic effects, 
including magnetic airborne detection. 

OEMsr-315 

Goodyear Aircraft Corp. 

Akron, Ohio 

Studies and experimental investigations 
looking toward the development of stream- 


lined serial housings for magnetic detec- 
tion equipment, including windtunnel and 
aircraft tests. 


146 


CONFIDENTIAL 


SERVICE PROJECT NUMBERS 

The projects listed below were transmitted to the Executive 
Secretary, National Defense Research Committee [NDRC], 
from the War or Navy Department through either the War 
Department Liaison Officer for NDRC or the Office of Re- 
search and Inventions (formerly the Coordinator of Re- 
search and Development), Navy Department. 


Service 


Project 

Number 

Subject 


AC-82 
NA-120 
Ext. NA-120 

Ext. NA-120 
Ext. NA-120 
Ext. NA-120 

Ext. NA-120 
Ext. NA-120 

NA-143 

NS-230 


Special MAD project for Fifth Air Force. 

Magnetic detection form aircraft. 

Arrangements for measurement of time variations in 
the magnetic field of the earth. 

Construction of a magnetic attack trainer. 

Requirements for CM-2/ASQ-2B equipments (39). 

Four sets of bulk spares for the CM-2/ASQ-2B equip- 
ments. 

Request for six AN/ASQ-IA towed birds. 

MAD “Bird” for naval airship training and experi- 
mental command. 

A preliminary investigation of the possibilities and 
limitations of using MAD for BTO. 

Reduction of interference on magnetic detection loops. 


CONFIDENTIAL 


147 


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INDEX 


The subject indexes of all STR volumes are combined in a master index printed in a separate volume. For 
access to the index volume consult the Army or Navy Agency listed on the reverse of the half-title page. 


AC perm detector, 87, 88, 101 
Adjustable perm compensator, 87, 
96, 97 

Airborne Instruments Laboratory, 
summary of MAD work, 7- 
10 

Airplane magnetism, compensation 
see Magnetic compensation in 
aircraft 

AM-l/ASQ-1 detector circuit, 32 
AM-9/ASQ-1A amplifier, 42 
AM-36/ASQ eddy-current ampli- 
fier, 100 

Ammeter, proposed permalloy in- 
duction type, 102 
AN/ASQ 

see also MAD 

AN/ASQ components, suggested 
alternatives, 123-125 
carrier system for CM-1; 125 
feedback detector, 125 
three component detector-mag- 
netometer, 123 

wave train magnetometer, 125 
AN/ASQ-1 system 
assembly, 25 

automatic release of bombs or 
flares, 65 

background noise, 38-39 
click test, 32 
design factors, 20-25 
detectability limits, 20 
detector amplifier circuit, 32-35 
detector sensitivity, 22, 38 
driver unit, 29 
400 cycle oscillator, 29 
location of magnetometer head, 
24 

magnetic neutralizing circuit, 32 
magnetometer alignment circuits, 
36 

magnetometer head, 19 
maximum stabilizer error, 39 
noise generated in core material, 
23 

operation of system, 25-28 
orienting amplifier circuits, 36-38 
performance characteristics, 38 
power supply, 29 
serviceability, 40 
servo requirements, 22 
size limitations, 24 
suppression of parasitic oscilla- 
tions, 31 


terrestrial magnetic noise, 22 
training of operators, 108-123 
types of noise, 20-21 
use as navigational aid, 133 
use in detecting land targets, 
130-131 

voltage regulator, 29 
AN/ASQ-1 A system with universal 
head, 41-42 

AN/ASQ-2 dual automatic system, 
65-81 

lateral control and tripper cir- 
cuits, 68-76 

lateral indicator circuit, 76-77 
performance characteristics, 81 
principles of operation, 65-66 
sum and difference circuits, 66-68 
test signal generator, 80 
AN/ASQ-3 second harmonic MAD 
system, 5, 65 

Anti-hunt arrangement in MAD, 38 
ASQ systems 
see AN/ASQ 

Attack operation with MAD, 61 
Audible signals for MAD systems, 8 
Automatic-firing MAD systems, 65- 
82 

Bail structure for Towed Bird, 104 
Barkhausen discontinuities, 18 
Bell Telephone Laboratories 
(BTL), 3, 5 
Mark X MAD, 5 
scroll-shaped core for magnetom- 
eters, 19 

Blimp installations of MAD, 106 
Blimp model for MAT, 115 
Bomb hit indicator for MAT, 121 
Bomb release circuit in AN/ASQ-2; 
65, 75 

Bridge circuits in AN/ASQ-2; 67 
Bridge connection of magnetom- 
eters, 15 

British magnetic oil gradiometer 
system, 2 

Cables for towed bird, 104 
California Institute of Technology, 
3 

Cities, detection with MAD, 133 
Click test for MAD systems, 32 
Clover-leaf pattern for MAD oper- 
ations, 60, 92 


CM-l/ASQ-2 tripper unit, 81, 125 
CM-2/ASQ-2B 
bridge circuits, 67 
conditions for bomb release, 69 
controls, 77 
flare circuit, 73 
hand fire circuit, 74 
lateral control circuit, 68 
lateral indicator circuit, 76 
sum meter circuit, 67 
tripper circuit, 69 
Columbia University, summary of 
MAD development, 7-10 
Compensation methods for aircraft, 
magnetic 

see Magnetic compensation in 
aircraft 

Compensation trainer, 122 
Contour charts, magnetic anomaly 
see Signal studies, MAD 
Copper rings used for magnetic 
field compensation, 83, 84, 90 
Core noise in magnetometers, 18-19 
CP-2/ASQ-1 tripper unit, 82 

DC amplifier with saturable reactor 
elements, 6 

DC magnetometer permalloy, 101 
Demodulator, phase sensitive, 113 
Deperming permanent magnetic 
fields in an aircraft, 87, 88 
Detector circuits in AN/ASQ-1 ; 32 
Detector sensitivity in AN/ASQ-1; 
38 

Difference bridge in AN/ASQ-2 
system, 68 

Driver circuit for saturated-core 
magnetometers, 31 
DT-l/ASQ-1 magnetometer head, 
25, 41 

DT-3/ASQ-1 universal magnetom- 
eter head, 41 

DY4/ASQ-1 power unit, 28 
Dynamotor-filter circuit in AN/ 
ASQ-1; 28-29 

Earth’s field, fluctuations in, 126 
Earth inductor, used as magnetom- 
eter, 6 

Eddy-current amplifier, AM-36/ 
ASQ, 100 

Eddy-current compensation in air- 
craft, 89-90, 96, 97 


CONFIDENTIAL 


149 



Electronic compensating system 
for induced fields, 98 
Electronic eddy-current compensa- 
tor, 90 

Esterline-Angus recording milli- 
ammeter, 66, 77, 101, 103 

Feedback detector proposed for 
MAD systems, 125 
Field engineering for MAD, 107 
Flare model system for MAT, 119 
Flare release circuit for CM-2/ 
ASQ-2B, 73 

Float lights used with MAD, 63 

General Electric Company, MAD 
research, 5 

Geophysical surveying with MAD, 
134 

Gibraltar, MAD patrol of the 
Straits, 64 

Gulf Research and Development 
Company, 4-5 

Gyroscopically stabilized magne- 
tometer heads, 4, 7 

Hand fire circuit for CM-2/ASQ- 
2B, 74 

Harmonic type magnetic detectors, 
5, 19 

Helmholz coils, 127 
High-mu permalloy, 18 

Indicating system for MAT, 118 
Induced magnetic fields in aircraft, 
86, 97, 98 

Inductance of a coil with a ferro- 
magnetic core, 11 
Induction type d-c ammeter, 103 
Installation of MAD in aircraft 
see MAD installations; Magnetic 
compensation in aircraft 
Intervalometer, use in MAT, 121 

Jam Handy Organization, 123 

Land targets, use of MAD against, 
128 

Lateral control circuit in AN/ 
ASQ-1; 68 

Lateral indicator circuit for CM-2/ 
ASQ-2B; 76 

Lighter-than-air installations of 
MAD, 106 

MAD, historical survey, 4-10 
MAD installations 




INDEX 


see also Magnetic compensation 
in aircraft 

location of MAD head on air- 
craft, 84-86 

PBY tail cone installation, 93 
PBY wingtip installation, 93-95 
summary of all service installa- 
tions, 106-107 

towed bird method, 103-106 
MAD Mark I 
components, 4 
installation in blimp, 5 
reduction of noise sources, 5 
MAD Mark II, 5 
MAD Mark IV, 7 
MAD Mark IV B-1 ; 7 
MAD Mark IV B-2; 8, 42, 106 
MAD Mark V, 7 

MAD Mark X ( AN/ASQ-3) , 5, 65 
MAD signal types 

see Signal studies, MAD 
MAD systems, service models 
see AN/ASQ designation 
MAD tactics, 60-64 
MAD uses 

detection of cities, 133 
detection of gun batteries and 
field equipment, 128, 131 
geophysical surveying, 133 
navigational aid, 133 
tactics against submarines, 60- 
64 

Magnetic airborne detection of sub- 
marines and land targets 
see MAD; AN/ASQ 
Magnetic attack trainer, 108-122 
background noise production, 116 
blimp model, 115 
bomb hit indicator, 121 
detector model, 115 
flare model system, 119 
general description, 108 
indicating systems, 109, 118 
model blimp, 109 
model submarine, 115 
model tactics area, 109, 118 
motor systems for blimp and sub- 
marine motions, 110-114 
optical system, 119 
simulating effect of winds on 
blimp course, 114 
simulation of bombing attack, 
121 

sono buoy detection system 
model, 122 

Magnetic compensation in aircraft, 
83-103 

AC perm detector, 101 
adjustable perm compensator, 97 

compensation flights, 90 

4 



compensation trainer, 103 
DC magnetometer, 101 
eddy-current compensator, 100 
eddy-current fields, 90 
electronic compensating system 
for induced fields, 98 
induced magnetic field, 88 
induction magnetometer, 102 
non-electronic compensation, 83, 
84 

on aircraft wing, 84-86 
PBY tail cone installation of 
MAD, 93 

PBY wingtip installation, 93 
permanent fields, 87 
recompensation for changes dur- 
ing service, 95-96 
summary of methods, 97 
three component gradiometer, 
102 

Magnetic compensation trainer, 
103 

Magnetic core noise, 18-19 
Magnetic dip angle, 41 
Magnetic field of the earth, fluctu- 
ations, 126 

Magnetic geophysical survey 
flights, 134 

Magnetic gradiometer, two coil, 5 
Magnetic moments of submarines, 
20-21, 43 

Magnetic noise elimination from 
aircraft 

see Magnetic compensation in 
aircraft 

Magnetic noise in magnetometer 
cores, 8 

Magnetic Observatory, Tucson, 126 
Magnetic plotting table, 47 
Magnetic shielding with permalloy 
sheets, 127 

Magnetic stabilization of MAD 
magnetometer head, 7 
Magnetic target for MAD training, 
123 

Magnetometer, portable permalloy 
induction type, 102 
Magnetometer, saturated-core 
design factors, 17-19 
history of development, 11 
magnetic core noise, 18 
magnetometer bridge, 15 
sensitivity formulas, 16 
sensitivity-noise ratio for differ- 
ent core metals, 18 
spike pattern formation, 13-15 
theory, 11-17 
wave train type, 125 
Magnetometer alignment circuits, 
36 



Magnetometer head, universal type, 
41-42 

Magnetometer head with three 
mutually perpendicular ele- 
ments, 123-125 
MAT-3 

see Magnetic attack trainer 
Mineola Training School, 123 
Models for simulating submarine 
magnetism, 43-52, 53-58, 115 
Motor control system for MAT, 
110-114 

Motor field amplifier circuit in 
AN/ASQ-1; 32 

Mumetal for magnetometer cores, 
18 

Naval Ordnance Laboratory, 5, 103, 
133 

Navigation with aid of MAD, 133 
Noise generator unit for MAT, 116 
Noise levels in AN/ASQ-1; 38 
Noise reduction in AN/ASQ-1 ,* 22- 
24 

0-1/ASQ-l driver unit, 29 
Operator training, MAD 
see Magnetic attack trainer 
Orienting amplifier circuits, AN/ 
ASQ-1; 36-38 

Oscillator circuit for AN/ASQ-1; 
29 

Pantograph tactics trainer, 122 
PBY installations on MAD, 93-95 
Peak position charts, 58 
Perm compensation procedure for 
aircraft, 97 

Perm compensator, adjustable, 87, 
96, 97 

Perm detector, 87, 88, 101 
Permalloy cores for magnetom- 
eters, 6, 11, 18 

Permalloy reactors as circuit ele- 
ments, 6 

Permalloy strips for neutralizing 
induced fields in aircraft, 88 
Permalloy-shielded test volumes, 
127 

Permanent magnetic fields in air- 
craft, 86, 97 

Perminvar for magnetometer cores, 
18 

Pitch and roll indicator, magnetic, 
103 

Polar magnetometer head for 
MAD, 25 

Power and driver circuits for 
AN/ASQ-1, 28 


Production rate of MAD systems, 
AIL, 126 


Stabilizer control circuit, MAD, 28 
Stabilizing magnetometers, MAD, 
22 


Quonset Point, tests of MAD towed 
bird, 106 

RC filters, response characteristics, 
126 

Recommendations for further re- 
search 

see AN/ASQ components, sug- 
gested alternatives 

Retro-fired bombs and flares with 
MAD, 63 

Right-left indicator in AN/ASQ-2; 
65 


Stabilization precision in AN/ 
ASQ-1; 39 

Steel structures, detection by MAD, 
132 

Steering control systems for MAT, 
114 

“Stinger” installation of MAD, 
106 

Submarine detection from aircraft 
see MAD 

Submarine magnetic field patterns 
see Signal studies, MAD 
Submarine magnetic moments, 20- 


Rules for recognizing submarine 
signals on MAD, 60 

San Diego School for MAD, 123 

Saturated-core magnetometers 
see Magnetometers, saturated- 
core 

Scaling methods for magnetic sig- 
nal studies, 44 

Search and attack with MAD, 61 

Sensitivity formulas for saturated- 
core magnetometers, 16 

Serviceability of AN/ASQ-1; 40 

Signal simulator for MAD testing, 
80, 127 

Signal studies, MAD, 43-64 
calibration of submarine model 
coils, 48 

dynamic submarine signals simu- 
lated from models, 58-60 
factors determining signals, 43 
magnetic plotting table, 47 
models for plotting dynamic 

MAD signals, 53-58 
models for plotting static con- 
tour charts, 43-52 
peak position charts, 58 
rules for recognizing submarine 
signals, 60 

submarine anomaly contour 

charts, 52-53 

submarine magnetic pattern 

types, 53 

sum and difference contour 

charts, 52-53 

Slicks used in MAD operations, 63 

Sono buoy model for MAT, 109, 
122 

Sperry Gyroscope Company, 1, 4 
MAD Mark V, 7 

Spike pattern in MAD systems, 13- 
17, 26, 32 

Spurious signals recorded by MAD, 
83 


21, 43 

Submarine magnetic moments, 
models for simulation, 43-52, 
53-58, 115 

Sum and difference MAD contour 
charts, 52-53 

Sum meter circuit in AN/ASQ-2; 
67 

Survey of MAD work, 1-10 

Tactics with MAD, 60-64 
Tailcone installations of MAD, 106 
Terrestrial magnetic noise, 22 
Three-component gradiometer, 102 
Threshold control in CM-2/ASQ- 
2B, 77 

Time index of an MAD signal, 60 
Towed bird MAD system, 8, 103- 
106 

cable attachment, 104 
damping motion of bird, 104 
strut suspension, 104 
tail structure, 104 
tests at Quonset Point, 106 
Trainer for MAD operators, 122 
see also Magnetic attack trainers 
Trainer for magnetic compensation 
techniques, 103 
Training films for MAD, 123 
Training in MAD maintenance, 122 
Tripper circuit for CM-l/ASQ-2; 
81 

Tripper circuit for CM-2/ASQ-2B. 
bomb circuit, 76 
functions, 69 
electronic switch, 71, 72 
frequency discriminating net- 
work, 71 

impedance transformer, 71, 72 
relay, 74 
time delay, 73 

Tripper circuit CP-2/ASQ-1; 82 
Tripper systems for MAD, princi- 
ples, 10, 65 




152 




TS-160/ASQ-2 MAD signal simula- 
tor, 80 

Universal magnetometer head, 41- 
42 


Vacquier saturated core magnetom- 
eter, 1, 4 

Voltage regulator for AN/ASQ-1; 
29 


Wave train magnetometer, 125 
Western Electric Company, 1, 5 
Wing installation of MAD head, 
84 



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